Initial support for ad hoc recipes (still work in progress)

21 files changed, 9222 insertions, 0 deletions

diff --git a/libbuild2/script/builtin-options.cxx b/libbuild2/script/builtin-options.cxx
new file mode 100644
index 0000000..2002764
--- /dev/null
+++ b/libbuild2/script/builtin-options.cxx
@@ -0,0 +1,661 @@
+// -*- C++ -*-
+//
+// This file was generated by CLI, a command line interface
+// compiler for C++.
+//
+
+// Begin prologue.
+//
+//
+// End prologue.
+
+#include <libbuild2/script/builtin-options.hxx>
+
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+#include <ostream>
+#include <sstream>
+
+namespace build2
+{
+  namespace script
+  {
+    namespace cli
+    {
+      // unknown_option
+      //
+      unknown_option::
+      ~unknown_option () throw ()
+      {
+      }
+
+      void unknown_option::
+      print (::std::ostream& os) const
+      {
+        os << "unknown option '" << option ().c_str () << "'";
+      }
+
+      const char* unknown_option::
+      what () const throw ()
+      {
+        return "unknown option";
+      }
+
+      // unknown_argument
+      //
+      unknown_argument::
+      ~unknown_argument () throw ()
+      {
+      }
+
+      void unknown_argument::
+      print (::std::ostream& os) const
+      {
+        os << "unknown argument '" << argument ().c_str () << "'";
+      }
+
+      const char* unknown_argument::
+      what () const throw ()
+      {
+        return "unknown argument";
+      }
+
+      // missing_value
+      //
+      missing_value::
+      ~missing_value () throw ()
+      {
+      }
+
+      void missing_value::
+      print (::std::ostream& os) const
+      {
+        os << "missing value for option '" << option ().c_str () << "'";
+      }
+
+      const char* missing_value::
+      what () const throw ()
+      {
+        return "missing option value";
+      }
+
+      // invalid_value
+      //
+      invalid_value::
+      ~invalid_value () throw ()
+      {
+      }
+
+      void invalid_value::
+      print (::std::ostream& os) const
+      {
+        os << "invalid value '" << value ().c_str () << "' for option '"
+           << option ().c_str () << "'";
+
+        if (!message ().empty ())
+          os << ": " << message ().c_str ();
+      }
+
+      const char* invalid_value::
+      what () const throw ()
+      {
+        return "invalid option value";
+      }
+
+      // eos_reached
+      //
+      void eos_reached::
+      print (::std::ostream& os) const
+      {
+        os << what ();
+      }
+
+      const char* eos_reached::
+      what () const throw ()
+      {
+        return "end of argument stream reached";
+      }
+
+      // scanner
+      //
+      scanner::
+      ~scanner ()
+      {
+      }
+
+      // argv_scanner
+      //
+      bool argv_scanner::
+      more ()
+      {
+        return i_ < argc_;
+      }
+
+      const char* argv_scanner::
+      peek ()
+      {
+        if (i_ < argc_)
+          return argv_[i_];
+        else
+          throw eos_reached ();
+      }
+
+      const char* argv_scanner::
+      next ()
+      {
+        if (i_ < argc_)
+        {
+          const char* r (argv_[i_]);
+
+          if (erase_)
+          {
+            for (int i (i_ + 1); i < argc_; ++i)
+              argv_[i - 1] = argv_[i];
+
+            --argc_;
+            argv_[argc_] = 0;
+          }
+          else
+            ++i_;
+
+          return r;
+        }
+        else
+          throw eos_reached ();
+      }
+
+      void argv_scanner::
+      skip ()
+      {
+        if (i_ < argc_)
+          ++i_;
+        else
+          throw eos_reached ();
+      }
+
+      // vector_scanner
+      //
+      bool vector_scanner::
+      more ()
+      {
+        return i_ < v_.size ();
+      }
+
+      const char* vector_scanner::
+      peek ()
+      {
+        if (i_ < v_.size ())
+          return v_[i_].c_str ();
+        else
+          throw eos_reached ();
+      }
+
+      const char* vector_scanner::
+      next ()
+      {
+        if (i_ < v_.size ())
+          return v_[i_++].c_str ();
+        else
+          throw eos_reached ();
+      }
+
+      void vector_scanner::
+      skip ()
+      {
+        if (i_ < v_.size ())
+          ++i_;
+        else
+          throw eos_reached ();
+      }
+
+      template <typename X>
+      struct parser
+      {
+        static void
+        parse (X& x, bool& xs, scanner& s)
+        {
+          using namespace std;
+
+          const char* o (s.next ());
+          if (s.more ())
+          {
+            string v (s.next ());
+            istringstream is (v);
+            if (!(is >> x && is.peek () == istringstream::traits_type::eof ()))
+              throw invalid_value (o, v);
+          }
+          else
+            throw missing_value (o);
+
+          xs = true;
+        }
+      };
+
+      template <>
+      struct parser<bool>
+      {
+        static void
+        parse (bool& x, scanner& s)
+        {
+          s.next ();
+          x = true;
+        }
+      };
+
+      template <>
+      struct parser<std::string>
+      {
+        static void
+        parse (std::string& x, bool& xs, scanner& s)
+        {
+          const char* o (s.next ());
+
+          if (s.more ())
+            x = s.next ();
+          else
+            throw missing_value (o);
+
+          xs = true;
+        }
+      };
+
+      template <typename X>
+      struct parser<std::vector<X> >
+      {
+        static void
+        parse (std::vector<X>& c, bool& xs, scanner& s)
+        {
+          X x;
+          bool dummy;
+          parser<X>::parse (x, dummy, s);
+          c.push_back (x);
+          xs = true;
+        }
+      };
+
+      template <typename X>
+      struct parser<std::set<X> >
+      {
+        static void
+        parse (std::set<X>& c, bool& xs, scanner& s)
+        {
+          X x;
+          bool dummy;
+          parser<X>::parse (x, dummy, s);
+          c.insert (x);
+          xs = true;
+        }
+      };
+
+      template <typename K, typename V>
+      struct parser<std::map<K, V> >
+      {
+        static void
+        parse (std::map<K, V>& m, bool& xs, scanner& s)
+        {
+          const char* o (s.next ());
+
+          if (s.more ())
+          {
+            std::string ov (s.next ());
+            std::string::size_type p = ov.find ('=');
+
+            K k = K ();
+            V v = V ();
+            std::string kstr (ov, 0, p);
+            std::string vstr (ov, (p != std::string::npos ? p + 1 : ov.size ()));
+
+            int ac (2);
+            char* av[] = 
+            {
+              const_cast<char*> (o), 0
+            };
+
+            bool dummy;
+            if (!kstr.empty ())
+            {
+              av[1] = const_cast<char*> (kstr.c_str ());
+              argv_scanner s (0, ac, av);
+              parser<K>::parse (k, dummy, s);
+            }
+
+            if (!vstr.empty ())
+            {
+              av[1] = const_cast<char*> (vstr.c_str ());
+              argv_scanner s (0, ac, av);
+              parser<V>::parse (v, dummy, s);
+            }
+
+            m[k] = v;
+          }
+          else
+            throw missing_value (o);
+
+          xs = true;
+        }
+      };
+
+      template <typename X, typename T, T X::*M>
+      void
+      thunk (X& x, scanner& s)
+      {
+        parser<T>::parse (x.*M, s);
+      }
+
+      template <typename X, typename T, T X::*M, bool X::*S>
+      void
+      thunk (X& x, scanner& s)
+      {
+        parser<T>::parse (x.*M, x.*S, s);
+      }
+    }
+  }
+}
+
+#include <map>
+#include <cstring>
+
+namespace build2
+{
+  namespace script
+  {
+    // set_options
+    //
+
+    set_options::
+    set_options ()
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+    }
+
+    set_options::
+    set_options (int& argc,
+                 char** argv,
+                 bool erase,
+                 ::build2::script::cli::unknown_mode opt,
+                 ::build2::script::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::script::cli::argv_scanner s (argc, argv, erase);
+      _parse (s, opt, arg);
+    }
+
+    set_options::
+    set_options (int start,
+                 int& argc,
+                 char** argv,
+                 bool erase,
+                 ::build2::script::cli::unknown_mode opt,
+                 ::build2::script::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::script::cli::argv_scanner s (start, argc, argv, erase);
+      _parse (s, opt, arg);
+    }
+
+    set_options::
+    set_options (int& argc,
+                 char** argv,
+                 int& end,
+                 bool erase,
+                 ::build2::script::cli::unknown_mode opt,
+                 ::build2::script::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::script::cli::argv_scanner s (argc, argv, erase);
+      _parse (s, opt, arg);
+      end = s.end ();
+    }
+
+    set_options::
+    set_options (int start,
+                 int& argc,
+                 char** argv,
+                 int& end,
+                 bool erase,
+                 ::build2::script::cli::unknown_mode opt,
+                 ::build2::script::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::script::cli::argv_scanner s (start, argc, argv, erase);
+      _parse (s, opt, arg);
+      end = s.end ();
+    }
+
+    set_options::
+    set_options (::build2::script::cli::scanner& s,
+                 ::build2::script::cli::unknown_mode opt,
+                 ::build2::script::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      _parse (s, opt, arg);
+    }
+
+    typedef
+    std::map<std::string, void (*) (set_options&, ::build2::script::cli::scanner&)>
+    _cli_set_options_map;
+
+    static _cli_set_options_map _cli_set_options_map_;
+
+    struct _cli_set_options_map_init
+    {
+      _cli_set_options_map_init ()
+      {
+        _cli_set_options_map_["--exact"] = 
+        &::build2::script::cli::thunk< set_options, bool, &set_options::exact_ >;
+        _cli_set_options_map_["-e"] = 
+        &::build2::script::cli::thunk< set_options, bool, &set_options::exact_ >;
+        _cli_set_options_map_["--newline"] = 
+        &::build2::script::cli::thunk< set_options, bool, &set_options::newline_ >;
+        _cli_set_options_map_["-n"] = 
+        &::build2::script::cli::thunk< set_options, bool, &set_options::newline_ >;
+        _cli_set_options_map_["--whitespace"] = 
+        &::build2::script::cli::thunk< set_options, bool, &set_options::whitespace_ >;
+        _cli_set_options_map_["-w"] = 
+        &::build2::script::cli::thunk< set_options, bool, &set_options::whitespace_ >;
+      }
+    };
+
+    static _cli_set_options_map_init _cli_set_options_map_init_;
+
+    bool set_options::
+    _parse (const char* o, ::build2::script::cli::scanner& s)
+    {
+      _cli_set_options_map::const_iterator i (_cli_set_options_map_.find (o));
+
+      if (i != _cli_set_options_map_.end ())
+      {
+        (*(i->second)) (*this, s);
+        return true;
+      }
+
+      return false;
+    }
+
+    bool set_options::
+    _parse (::build2::script::cli::scanner& s,
+            ::build2::script::cli::unknown_mode opt_mode,
+            ::build2::script::cli::unknown_mode arg_mode)
+    {
+      // Can't skip combined flags (--no-combined-flags).
+      //
+      assert (opt_mode != ::build2::script::cli::unknown_mode::skip);
+
+      bool r = false;
+      bool opt = true;
+
+      while (s.more ())
+      {
+        const char* o = s.peek ();
+
+        if (std::strcmp (o, "--") == 0)
+        {
+          opt = false;
+          s.skip ();
+          r = true;
+          continue;
+        }
+
+        if (opt)
+        {
+          if (_parse (o, s))
+          {
+            r = true;
+            continue;
+          }
+
+          if (std::strncmp (o, "-", 1) == 0 && o[1] != '\0')
+          {
+            // Handle combined option values.
+            //
+            std::string co;
+            if (const char* v = std::strchr (o, '='))
+            {
+              co.assign (o, 0, v - o);
+              ++v;
+
+              int ac (2);
+              char* av[] =
+              {
+                const_cast<char*> (co.c_str ()),
+                const_cast<char*> (v)
+              };
+
+              ::build2::script::cli::argv_scanner ns (0, ac, av);
+
+              if (_parse (co.c_str (), ns))
+              {
+                // Parsed the option but not its value?
+                //
+                if (ns.end () != 2)
+                  throw ::build2::script::cli::invalid_value (co, v);
+
+                s.next ();
+                r = true;
+                continue;
+              }
+              else
+              {
+                // Set the unknown option and fall through.
+                //
+                o = co.c_str ();
+              }
+            }
+
+            // Handle combined flags.
+            //
+            char cf[3];
+            {
+              const char* p = o + 1;
+              for (; *p != '\0'; ++p)
+              {
+                if (!((*p >= 'a' && *p <= 'z') ||
+                      (*p >= 'A' && *p <= 'Z') ||
+                      (*p >= '0' && *p <= '9')))
+                  break;
+              }
+
+              if (*p == '\0')
+              {
+                for (p = o + 1; *p != '\0'; ++p)
+                {
+                  std::strcpy (cf, "-");
+                  cf[1] = *p;
+                  cf[2] = '\0';
+
+                  int ac (1);
+                  char* av[] = 
+                  {
+                    cf
+                  };
+
+                  ::build2::script::cli::argv_scanner ns (0, ac, av);
+
+                  if (!_parse (cf, ns))
+                    break;
+                }
+
+                if (*p == '\0')
+                {
+                  // All handled.
+                  //
+                  s.next ();
+                  r = true;
+                  continue;
+                }
+                else
+                {
+                  // Set the unknown option and fall through.
+                  //
+                  o = cf;
+                }
+              }
+            }
+
+            switch (opt_mode)
+            {
+              case ::build2::script::cli::unknown_mode::skip:
+              {
+                s.skip ();
+                r = true;
+                continue;
+              }
+              case ::build2::script::cli::unknown_mode::stop:
+              {
+                break;
+              }
+              case ::build2::script::cli::unknown_mode::fail:
+              {
+                throw ::build2::script::cli::unknown_option (o);
+              }
+            }
+
+            break;
+          }
+        }
+
+        switch (arg_mode)
+        {
+          case ::build2::script::cli::unknown_mode::skip:
+          {
+            s.skip ();
+            r = true;
+            continue;
+          }
+          case ::build2::script::cli::unknown_mode::stop:
+          {
+            break;
+          }
+          case ::build2::script::cli::unknown_mode::fail:
+          {
+            throw ::build2::script::cli::unknown_argument (o);
+          }
+        }
+
+        break;
+      }
+
+      return r;
+    }
+  }
+}
+
+// Begin epilogue.
+//
+//
+// End epilogue.
+
diff --git a/libbuild2/script/builtin-options.hxx b/libbuild2/script/builtin-options.hxx
new file mode 100644
index 0000000..5a3f153
--- /dev/null
+++ b/libbuild2/script/builtin-options.hxx
@@ -0,0 +1,339 @@
+// -*- C++ -*-
+//
+// This file was generated by CLI, a command line interface
+// compiler for C++.
+//
+
+#ifndef LIBBUILD2_SCRIPT_BUILTIN_OPTIONS_HXX
+#define LIBBUILD2_SCRIPT_BUILTIN_OPTIONS_HXX
+
+// Begin prologue.
+//
+//
+// End prologue.
+
+#include <vector>
+#include <iosfwd>
+#include <string>
+#include <cstddef>
+#include <exception>
+
+#ifndef CLI_POTENTIALLY_UNUSED
+#  if defined(_MSC_VER) || defined(__xlC__)
+#    define CLI_POTENTIALLY_UNUSED(x) (void*)&x
+#  else
+#    define CLI_POTENTIALLY_UNUSED(x) (void)x
+#  endif
+#endif
+
+namespace build2
+{
+  namespace script
+  {
+    namespace cli
+    {
+      class unknown_mode
+      {
+        public:
+        enum value
+        {
+          skip,
+          stop,
+          fail
+        };
+
+        unknown_mode (value);
+
+        operator value () const 
+        {
+          return v_;
+        }
+
+        private:
+        value v_;
+      };
+
+      // Exceptions.
+      //
+
+      class exception: public std::exception
+      {
+        public:
+        virtual void
+        print (::std::ostream&) const = 0;
+      };
+
+      ::std::ostream&
+      operator<< (::std::ostream&, const exception&);
+
+      class unknown_option: public exception
+      {
+        public:
+        virtual
+        ~unknown_option () throw ();
+
+        unknown_option (const std::string& option);
+
+        const std::string&
+        option () const;
+
+        virtual void
+        print (::std::ostream&) const;
+
+        virtual const char*
+        what () const throw ();
+
+        private:
+        std::string option_;
+      };
+
+      class unknown_argument: public exception
+      {
+        public:
+        virtual
+        ~unknown_argument () throw ();
+
+        unknown_argument (const std::string& argument);
+
+        const std::string&
+        argument () const;
+
+        virtual void
+        print (::std::ostream&) const;
+
+        virtual const char*
+        what () const throw ();
+
+        private:
+        std::string argument_;
+      };
+
+      class missing_value: public exception
+      {
+        public:
+        virtual
+        ~missing_value () throw ();
+
+        missing_value (const std::string& option);
+
+        const std::string&
+        option () const;
+
+        virtual void
+        print (::std::ostream&) const;
+
+        virtual const char*
+        what () const throw ();
+
+        private:
+        std::string option_;
+      };
+
+      class invalid_value: public exception
+      {
+        public:
+        virtual
+        ~invalid_value () throw ();
+
+        invalid_value (const std::string& option,
+                       const std::string& value,
+                       const std::string& message = std::string ());
+
+        const std::string&
+        option () const;
+
+        const std::string&
+        value () const;
+
+        const std::string&
+        message () const;
+
+        virtual void
+        print (::std::ostream&) const;
+
+        virtual const char*
+        what () const throw ();
+
+        private:
+        std::string option_;
+        std::string value_;
+        std::string message_;
+      };
+
+      class eos_reached: public exception
+      {
+        public:
+        virtual void
+        print (::std::ostream&) const;
+
+        virtual const char*
+        what () const throw ();
+      };
+
+      // Command line argument scanner interface.
+      //
+      // The values returned by next() are guaranteed to be valid
+      // for the two previous arguments up until a call to a third
+      // peek() or next().
+      //
+      class scanner
+      {
+        public:
+        virtual
+        ~scanner ();
+
+        virtual bool
+        more () = 0;
+
+        virtual const char*
+        peek () = 0;
+
+        virtual const char*
+        next () = 0;
+
+        virtual void
+        skip () = 0;
+      };
+
+      class argv_scanner: public scanner
+      {
+        public:
+        argv_scanner (int& argc, char** argv, bool erase = false);
+        argv_scanner (int start, int& argc, char** argv, bool erase = false);
+
+        int
+        end () const;
+
+        virtual bool
+        more ();
+
+        virtual const char*
+        peek ();
+
+        virtual const char*
+        next ();
+
+        virtual void
+        skip ();
+
+        private:
+        int i_;
+        int& argc_;
+        char** argv_;
+        bool erase_;
+      };
+
+      class vector_scanner: public scanner
+      {
+        public:
+        vector_scanner (const std::vector<std::string>&, std::size_t start = 0);
+
+        std::size_t
+        end () const;
+
+        void
+        reset (std::size_t start = 0);
+
+        virtual bool
+        more ();
+
+        virtual const char*
+        peek ();
+
+        virtual const char*
+        next ();
+
+        virtual void
+        skip ();
+
+        private:
+        const std::vector<std::string>& v_;
+        std::size_t i_;
+      };
+
+      template <typename X>
+      struct parser;
+    }
+  }
+}
+
+namespace build2
+{
+  namespace script
+  {
+    class set_options
+    {
+      public:
+      set_options ();
+
+      set_options (int& argc,
+                   char** argv,
+                   bool erase = false,
+                   ::build2::script::cli::unknown_mode option = ::build2::script::cli::unknown_mode::fail,
+                   ::build2::script::cli::unknown_mode argument = ::build2::script::cli::unknown_mode::stop);
+
+      set_options (int start,
+                   int& argc,
+                   char** argv,
+                   bool erase = false,
+                   ::build2::script::cli::unknown_mode option = ::build2::script::cli::unknown_mode::fail,
+                   ::build2::script::cli::unknown_mode argument = ::build2::script::cli::unknown_mode::stop);
+
+      set_options (int& argc,
+                   char** argv,
+                   int& end,
+                   bool erase = false,
+                   ::build2::script::cli::unknown_mode option = ::build2::script::cli::unknown_mode::fail,
+                   ::build2::script::cli::unknown_mode argument = ::build2::script::cli::unknown_mode::stop);
+
+      set_options (int start,
+                   int& argc,
+                   char** argv,
+                   int& end,
+                   bool erase = false,
+                   ::build2::script::cli::unknown_mode option = ::build2::script::cli::unknown_mode::fail,
+                   ::build2::script::cli::unknown_mode argument = ::build2::script::cli::unknown_mode::stop);
+
+      set_options (::build2::script::cli::scanner&,
+                   ::build2::script::cli::unknown_mode option = ::build2::script::cli::unknown_mode::fail,
+                   ::build2::script::cli::unknown_mode argument = ::build2::script::cli::unknown_mode::stop);
+
+      // Option accessors.
+      //
+      const bool&
+      exact () const;
+
+      const bool&
+      newline () const;
+
+      const bool&
+      whitespace () const;
+
+      // Implementation details.
+      //
+      protected:
+      bool
+      _parse (const char*, ::build2::script::cli::scanner&);
+
+      private:
+      bool
+      _parse (::build2::script::cli::scanner&,
+              ::build2::script::cli::unknown_mode option,
+              ::build2::script::cli::unknown_mode argument);
+
+      public:
+      bool exact_;
+      bool newline_;
+      bool whitespace_;
+    };
+  }
+}
+
+#include <libbuild2/script/builtin-options.ixx>
+
+// Begin epilogue.
+//
+//
+// End epilogue.
+
+#endif // LIBBUILD2_SCRIPT_BUILTIN_OPTIONS_HXX
diff --git a/libbuild2/script/builtin-options.ixx b/libbuild2/script/builtin-options.ixx
new file mode 100644
index 0000000..dc59f98
--- /dev/null
+++ b/libbuild2/script/builtin-options.ixx
@@ -0,0 +1,182 @@
+// -*- C++ -*-
+//
+// This file was generated by CLI, a command line interface
+// compiler for C++.
+//
+
+// Begin prologue.
+//
+//
+// End prologue.
+
+#include <cassert>
+
+namespace build2
+{
+  namespace script
+  {
+    namespace cli
+    {
+      // unknown_mode
+      //
+      inline unknown_mode::
+      unknown_mode (value v)
+      : v_ (v)
+      {
+      }
+
+      // exception
+      //
+      inline ::std::ostream&
+      operator<< (::std::ostream& os, const exception& e)
+      {
+        e.print (os);
+        return os;
+      }
+
+      // unknown_option
+      //
+      inline unknown_option::
+      unknown_option (const std::string& option)
+      : option_ (option)
+      {
+      }
+
+      inline const std::string& unknown_option::
+      option () const
+      {
+        return option_;
+      }
+
+      // unknown_argument
+      //
+      inline unknown_argument::
+      unknown_argument (const std::string& argument)
+      : argument_ (argument)
+      {
+      }
+
+      inline const std::string& unknown_argument::
+      argument () const
+      {
+        return argument_;
+      }
+
+      // missing_value
+      //
+      inline missing_value::
+      missing_value (const std::string& option)
+      : option_ (option)
+      {
+      }
+
+      inline const std::string& missing_value::
+      option () const
+      {
+        return option_;
+      }
+
+      // invalid_value
+      //
+      inline invalid_value::
+      invalid_value (const std::string& option,
+                     const std::string& value,
+                     const std::string& message)
+      : option_ (option),
+        value_ (value),
+        message_ (message)
+      {
+      }
+
+      inline const std::string& invalid_value::
+      option () const
+      {
+        return option_;
+      }
+
+      inline const std::string& invalid_value::
+      value () const
+      {
+        return value_;
+      }
+
+      inline const std::string& invalid_value::
+      message () const
+      {
+        return message_;
+      }
+
+      // argv_scanner
+      //
+      inline argv_scanner::
+      argv_scanner (int& argc, char** argv, bool erase)
+      : i_ (1), argc_ (argc), argv_ (argv), erase_ (erase)
+      {
+      }
+
+      inline argv_scanner::
+      argv_scanner (int start, int& argc, char** argv, bool erase)
+      : i_ (start), argc_ (argc), argv_ (argv), erase_ (erase)
+      {
+      }
+
+      inline int argv_scanner::
+      end () const
+      {
+        return i_;
+      }
+
+      // vector_scanner
+      //
+      inline vector_scanner::
+      vector_scanner (const std::vector<std::string>& v, std::size_t i)
+      : v_ (v), i_ (i)
+      {
+      }
+
+      inline std::size_t vector_scanner::
+      end () const
+      {
+        return i_;
+      }
+
+      inline void vector_scanner::
+      reset (std::size_t i)
+      {
+        i_ = i;
+      }
+    }
+  }
+}
+
+namespace build2
+{
+  namespace script
+  {
+    // set_options
+    //
+
+    inline const bool& set_options::
+    exact () const
+    {
+      return this->exact_;
+    }
+
+    inline const bool& set_options::
+    newline () const
+    {
+      return this->newline_;
+    }
+
+    inline const bool& set_options::
+    whitespace () const
+    {
+      return this->whitespace_;
+    }
+  }
+}
+
+// Begin epilogue.
+//
+//
+// End epilogue.
diff --git a/libbuild2/script/builtin.cli b/libbuild2/script/builtin.cli
new file mode 100644
index 0000000..68db23e
--- /dev/null
+++ b/libbuild2/script/builtin.cli
@@ -0,0 +1,21 @@
+// file      : libbuild2/script/builtin.cli
+// license   : MIT; see accompanying LICENSE file
+
+// Note that options in this file are undocumented because we generate neither
+// the usage printing code nor man pages. Instead, they are documented in the
+// Testscript Language Manual's builtin descriptions.
+//
+namespace build2
+{
+  namespace script
+  {
+    // Pseudo-builtin options.
+    //
+    class set_options
+    {
+      bool --exact|-e;
+      bool --newline|-n;
+      bool --whitespace|-w;
+    };
+  }
+}
diff --git a/libbuild2/script/lexer+command-expansion.test.testscript b/libbuild2/script/lexer+command-expansion.test.testscript
new file mode 100644
index 0000000..f4d69d2
--- /dev/null
+++ b/libbuild2/script/lexer+command-expansion.test.testscript
@@ -0,0 +1,321 @@
+# file      : libbuild2/script/lexer+command-expansion.test.testscript
+# license   : MIT; see accompanying LICENSE file
+
+test.arguments = command-expansion
+
+: pass-redirect
+:
+{
+  : in
+  :
+  $* <:"0<|" >>EOO
+  '0'
+  <|
+  EOO
+
+  : arg-in
+  :
+  $* <:"0 <|" >>EOO
+  '0 '
+  <|
+  EOO
+
+  : out
+  :
+  $* <:"1>|" >>EOO
+  '1'
+  >|
+  EOO
+
+  : arg-out
+  :
+  $* <:"1 >|" >>EOO
+  '1 '
+  >|
+  EOO
+}
+
+: null-redirect
+:
+{
+  : in
+  :
+  $* <:"0<-" >>EOO
+  '0'
+  <-
+  EOO
+
+  : arg-in
+  :
+  $* <:"0 <-" >>EOO
+  '0 '
+  <-
+  EOO
+
+  : out
+  :
+  $* <:"1>-" >>EOO
+  '1'
+  >-
+  EOO
+
+  : arg-out
+  :
+  $* <:"1 >-" >>EOO
+  '1 '
+  >-
+  EOO
+}
+
+: trace-redirect
+:
+{
+  : out
+  :
+  $* <:"1>!" >>EOO
+  '1'
+  >!
+  EOO
+
+  : arg-out
+  :
+  $* <:"1 >!" >>EOO
+  '1 '
+  >!
+  EOO
+}
+
+: merge-redirect
+:
+{
+  : out
+  :
+  $* <:"1>&2" >>EOO
+  '1'
+  >&
+  '2'
+  EOO
+
+  : arg-out
+  :
+  $* <:"1 >&2" >>EOO
+  '1 '
+  >&
+  '2'
+  EOO
+}
+
+: str-redirect
+:
+{
+  : in
+  :
+  {
+    : newline
+    :
+    $* <:"0<<<=a b" >>EOO
+    '0'
+    <<<=
+    'a b'
+    EOO
+
+    : no-newline
+    :
+    $* <:"0<<<=:a b" >>EOO
+    '0'
+    <<<=:
+    'a b'
+    EOO
+  }
+
+  : in-alias
+  :
+  {
+    : newline
+    :
+    $* <:"0<<<a b" >>EOO
+    '0'
+    <<<
+    'a b'
+    EOO
+
+    : no-newline
+    :
+    $* <:"0<<<:a b" >>EOO
+    '0'
+    <<<:
+    'a b'
+    EOO
+  }
+
+  : out
+  :
+  {
+    : newline
+    :
+    $* <:"1>>>?a b" >>EOO
+    '1'
+    >>>?
+    'a b'
+    EOO
+
+    : no-newline
+    :
+    $* <:"1>>>?:a b" >>EOO
+    '1'
+    >>>?:
+    'a b'
+    EOO
+  }
+}
+
+: doc-redirect
+:
+{
+  : in
+  :
+  {
+    : newline
+    :
+    $* <:"0<<=E O I" >>EOO
+    '0'
+    <<=
+    'E O I'
+    EOO
+
+    : no-newline
+    :
+    $* <:"0<<=:E O I" >>EOO
+    '0'
+    <<=:
+    'E O I'
+    EOO
+  }
+
+  : in-alias
+  :
+  {
+    : newline
+    :
+    $* <:"0<<E O I" >>EOO
+    '0'
+    <<
+    'E O I'
+    EOO
+
+    : no-newline
+    :
+    $* <:"0<<:E O I" >>EOO
+    '0'
+    <<:
+    'E O I'
+    EOO
+  }
+
+  : out
+  :
+  {
+    : newline
+    :
+    $* <:"1>>?E O O" >>EOO
+    '1'
+    >>?
+    'E O O'
+    EOO
+
+    : no-newline
+    :
+    $* <:"1>>?:E O O" >>EOO
+    '1'
+    >>?:
+    'E O O'
+    EOO
+  }
+}
+
+: file-redirect
+:
+{
+  : in
+  :
+  $* <:"0<=a b" >>EOO
+  '0'
+  <=
+  'a b'
+  EOO
+
+  : in-alias
+  :
+  $* <:"0<a b" >>EOO
+  '0'
+  <
+  'a b'
+  EOO
+
+  : out
+  :
+  $* <:"1>=a b" >>EOO
+  '1'
+  >=
+  'a b'
+  EOO
+
+ : out-alias
+  :
+  $* <:"1>a b" >>EOO
+  '1'
+  >
+  'a b'
+  EOO
+
+  : out-app
+  :
+  $* <:"1>+a b" >>EOO
+  '1'
+  >+
+  'a b'
+  EOO
+
+  : out-app-alias
+  :
+  $* <:"1>>a b" >>EOO
+  '1'
+  >>
+  'a b'
+  EOO
+}
+
+: no-out-alias
+:
+$* <:"1>>>a b" >>EOO
+'1'
+>>
+>
+'a b'
+EOO
+
+
+: cleanup
+:
+{
+  : always
+  :
+  $* <:"&file" >>EOO
+  &
+  'file'
+  EOO
+
+  : maybe
+  :
+  $* <:"&?file" >>EOO
+  &?
+  'file'
+  EOO
+
+  : never
+  :
+  $* <:"&!file" >>EOO
+  &!
+  'file'
+  EOO
+}
diff --git a/libbuild2/script/lexer.cxx b/libbuild2/script/lexer.cxx
new file mode 100644
index 0000000..d78e999
--- /dev/null
+++ b/libbuild2/script/lexer.cxx
@@ -0,0 +1,431 @@
+// file      : libbuild2/script/lexer.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/script/lexer.hxx>
+
+#include <cstring> // strchr()
+
+using namespace std;
+
+namespace build2
+{
+  namespace script
+  {
+    using type = token_type;
+
+    void lexer::
+    mode (base_mode m, char ps, optional<const char*> esc, uintptr_t data)
+    {
+      bool a (false); // attributes
+
+      const char* s1 (nullptr);
+      const char* s2 (nullptr);
+
+      bool s (true); // space
+      bool n (true); // newline
+      bool q (true); // quotes
+
+      if (!esc)
+      {
+        assert (!state_.empty ());
+        esc = state_.top ().escapes;
+      }
+
+      switch (m)
+      {
+      case lexer_mode::command_expansion:
+        {
+          // Note that whitespaces are not word separators in this mode.
+          //
+          s1 = "|&<>";
+          s2 = "    ";
+          s = false;
+          break;
+        }
+      case lexer_mode::here_line_single:
+        {
+          // This one is like a single-quoted string except it treats
+          // newlines as a separator. We also treat quotes as literals.
+          //
+          // Note that it might be tempting to enable line continuation
+          // escapes. However, we will then have to also enable escaping of
+          // the backslash, which makes it a lot less tempting.
+          //
+          s1 = "\n";
+          s2 = " ";
+          esc = ""; // Disable escape sequences.
+          s = false;
+          q = false;
+          break;
+        }
+      case lexer_mode::here_line_double:
+        {
+          // This one is like a double-quoted string except it treats
+          // newlines as a separator. We also treat quotes as literals.
+          //
+          s1 = "$(\n";
+          s2 = "   ";
+          s = false;
+          q = false;
+          break;
+        }
+      default:
+        {
+          // Make sure pair separators are only enabled where we expect
+          // them.
+          //
+          // @@ Should we disable pair separators in the eval mode?
+          //
+          assert (ps == '\0' ||
+                  m == lexer_mode::eval ||
+                  m == lexer_mode::attribute_value);
+
+          base_lexer::mode (m, ps, esc);
+          return;
+        }
+      }
+
+      assert (ps == '\0');
+      state_.push (state {m, data, nullopt, a, ps, s, n, q, *esc, s1, s2});
+    }
+
+    token lexer::
+    next ()
+    {
+      token r;
+
+      switch (state_.top ().mode)
+      {
+      case lexer_mode::command_expansion:
+      case lexer_mode::here_line_single:
+      case lexer_mode::here_line_double:
+        r = next_line ();
+        break;
+      default:
+        r = base_lexer::next ();
+        break;
+      }
+
+      if (r.qtype != quote_type::unquoted)
+        ++quoted_;
+
+      return r;
+    }
+
+    token lexer::
+    next_line ()
+    {
+      bool sep (skip_spaces ().first);
+
+      xchar c (get ());
+      uint64_t ln (c.line), cn (c.column);
+
+      const state& st (state_.top ());
+      lexer_mode m (st.mode);
+
+      auto make_token = [&sep, &m, ln, cn] (type t)
+      {
+        bool q (m == lexer_mode::here_line_double);
+
+        return token (t, string (), sep,
+                      (q ? quote_type::double_ : quote_type::unquoted), q,
+                      ln, cn,
+                      token_printer);
+      };
+
+      if (eos (c))
+        return make_token (type::eos);
+
+      // NOTE: remember to update mode() if adding new special characters.
+
+      if (m != lexer_mode::command_expansion)
+      {
+        switch (c)
+        {
+        case '\n':
+          {
+            sep = true; // Treat newline as always separated.
+            return make_token (type::newline);
+          }
+        }
+      }
+
+      if (m != lexer_mode::here_line_single)
+      {
+        switch (c)
+        {
+          // Variable expansion, function call, and evaluation context.
+          //
+        case '$': return make_token (type::dollar);
+        case '(': return make_token (type::lparen);
+        }
+      }
+
+      // Command operators.
+      //
+      if (m == lexer_mode::command_expansion)
+      {
+        if (optional<token> t = next_cmd_op (c, sep))
+          return move (*t);
+      }
+
+      // Otherwise it is a word.
+      //
+      unget (c);
+      return word (st, sep);
+    }
+
+    optional<token> lexer::
+    next_cmd_op (const xchar& c, bool sep)
+    {
+      auto make_token = [&sep, &c] (type t, string v = string ())
+      {
+        return token (t, move (v), sep,
+                      quote_type::unquoted, false,
+                      c.line, c.column,
+                      token_printer);
+      };
+
+      auto make_token_with_modifiers =
+        [&make_token, this] (type t,
+                             const char* mods,           // To recorgnize.
+                             const char* stop = nullptr) // To stop after.
+        {
+          string v;
+          if (mods != nullptr)
+          {
+            for (xchar p (peek ());
+                 (strchr (mods, p) != nullptr &&      // Modifier.
+                  strchr (v.c_str (), p) == nullptr); // Not already seen.
+                 p = peek ())
+            {
+              get ();
+              v += p;
+
+              if (stop != nullptr && strchr (stop, p) != nullptr)
+                break;
+            }
+          }
+
+          return make_token (t, move (v));
+        };
+
+      switch (c)
+      {
+        // |, ||
+        //
+      case '|':
+        {
+          if (peek () == '|')
+          {
+            get ();
+            return make_token (type::log_or);
+          }
+          else
+            return make_token (type::pipe);
+        }
+        // &, &&
+        //
+      case '&':
+        {
+          xchar p (peek ());
+
+          if (p == '&')
+          {
+            get ();
+            return make_token (type::log_and);
+          }
+
+          // These modifiers are mutually exclusive so stop after seeing
+          // either one.
+          //
+          return make_token_with_modifiers (type::clean, "!?", "!?");
+        }
+        // <
+        //
+      case '<':
+        {
+          optional<type> r;
+          xchar p (peek ());
+
+          if (p == '|' || p == '-' || p == '=' || p == '<') // <| <- <= <<
+          {
+            xchar c (get ());
+
+            switch (p)
+            {
+            case '|': return make_token (type::in_pass);    // <|
+            case '-': return make_token (type::in_null);    // <-
+            case '=': return make_token (type::in_file);    // <=
+            case '<':                                       // <<
+              {
+                p = peek ();
+
+                if (p == '=' || p == '<')                   // <<= <<<
+                {
+                  xchar c (get ());
+
+                  switch (p)
+                  {
+                  case '=':
+                    {
+                      r = type::in_doc;                     // <<=
+                      break;
+                    }
+                  case '<':
+                    {
+                      p = peek ();
+
+                      if (p == '=')
+                      {
+                        get ();
+                        r = type::in_str;                   // <<<=
+                      }
+
+                      if (!r && redirect_aliases.lll)
+                        r = type::in_lll;                   // <<<
+
+                      // We can still end up with the << or < redirect alias,
+                      // if any of them is present.
+                      //
+                      if (!r)
+                        unget (c);
+                    }
+
+                    break;
+                  }
+                }
+
+                if (!r && redirect_aliases.ll)
+                  r = type::in_ll;                          // <<
+
+                // We can still end up with the < redirect alias, if it is
+                // present.
+                //
+                if (!r)
+                  unget (c);
+
+                break;
+              }
+            }
+          }
+
+          if (!r && redirect_aliases.l)
+            r = type::in_l;                                 // <
+
+          if (!r)
+            return nullopt;
+
+          // Handle modifiers.
+          //
+          const char* mods (nullptr);
+
+          switch (redirect_aliases.resolve (*r))
+          {
+          case type::in_str:
+          case type::in_doc: mods = ":/"; break;
+          }
+
+          token t (make_token_with_modifiers (*r, mods));
+
+          return t;
+        }
+        // >
+        //
+      case '>':
+        {
+          optional<type> r;
+          xchar p (peek ());
+
+          if (p == '|' || p == '-' || p == '!' || p == '&' || // >| >- >! >&
+              p == '=' || p == '+' || p == '?' || p == '>')   // >= >+ >? >>
+          {
+            xchar c (get ());
+
+            switch (p)
+            {
+            case '|': return make_token (type::out_pass);     // >|
+            case '-': return make_token (type::out_null);     // >-
+            case '!': return make_token (type::out_trace);    // >!
+            case '&': return make_token (type::out_merge);    // >&
+            case '=': return make_token (type::out_file_ovr); // >=
+            case '+': return make_token (type::out_file_app); // >+
+            case '?': return make_token (type::out_file_cmp); // >?
+            case '>':                                         // >>
+              {
+                p = peek ();
+
+                if (p == '?' || p == '>')                     // >>? >>>
+                {
+                  xchar c (get ());
+
+                  switch (p)
+                  {
+                  case '?':
+                    {
+                      r = type::out_doc;                       // >>?
+                      break;
+                    }
+                  case '>':
+                    {
+                      p = peek ();
+
+                      if (p == '?')
+                      {
+                        get ();
+                        r = type::out_str;                     // >>>?
+                      }
+
+                      if (!r && redirect_aliases.ggg)
+                        r = type::out_ggg;                     // >>>
+
+                      // We can still end up with the >> or > redirect alias,
+                      // if any of themis present.
+                      //
+                      if (!r)
+                        unget (c);
+                    }
+
+                    break;
+                  }
+                }
+
+                if (!r && redirect_aliases.gg)
+                  r = type::out_gg;                          // >>
+
+                // We can still end up with the > redirect alias, if it is
+                // present.
+                //
+                if (!r)
+                  unget (c);
+
+                break;
+              }
+            }
+          }
+
+          if (!r && redirect_aliases.g)
+            r = type::out_g;                                 // >
+
+          if (!r)
+            return nullopt;
+
+          // Handle modifiers.
+          //
+          const char* mods (nullptr);
+          const char* stop (nullptr);
+
+          switch (redirect_aliases.resolve (*r))
+          {
+          case type::out_str:
+          case type::out_doc: mods = ":/~"; stop = "~"; break;
+          }
+
+          return make_token_with_modifiers (*r, mods, stop);
+        }
+      }
+
+      return nullopt;
+    }
+  }
+}
diff --git a/libbuild2/script/lexer.hxx b/libbuild2/script/lexer.hxx
new file mode 100644
index 0000000..dbfdfcc
--- /dev/null
+++ b/libbuild2/script/lexer.hxx
@@ -0,0 +1,139 @@
+// file      : libbuild2/script/lexer.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_SCRIPT_LEXER_HXX
+#define LIBBUILD2_SCRIPT_LEXER_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/lexer.hxx>
+
+#include <libbuild2/script/token.hxx>
+
+namespace build2
+{
+  namespace script
+  {
+    struct lexer_mode: build2::lexer_mode
+    {
+      using base_type = build2::lexer_mode;
+
+      enum
+      {
+        command_expansion = base_type::value_next,
+        here_line_single,
+        here_line_double,
+
+        value_next
+      };
+
+      lexer_mode () = default;
+      lexer_mode (value_type v): base_type (v) {}
+      lexer_mode (base_type v): base_type (v) {}
+    };
+
+    // Actual redirects (as tokens) for the the <, <<, <<<, and >, >>, >>>
+    // aliases.
+    //
+    struct redirect_aliases
+    {
+      optional<token_type> l;   // <
+      optional<token_type> ll;  // <<
+      optional<token_type> lll; // <<<
+      optional<token_type> g;   // >
+      optional<token_type> gg;  // >>
+      optional<token_type> ggg; // >>>
+
+      // If the token type is a redirect alias then return the token type it
+      // resolves to and the passed token type otherwise. Note that it's the
+      // caller's responsibility to make sure that the corresponding alias is
+      // present (normally by not recognizing absent aliases as tokens).
+      //
+      token_type
+      resolve (token_type t) const noexcept
+      {
+        switch (t)
+        {
+        case token_type::in_l:    assert (l);   return *l;
+        case token_type::in_ll:   assert (ll);  return *ll;
+        case token_type::in_lll:  assert (lll); return *lll;
+        case token_type::out_g:   assert (g);   return *g;
+        case token_type::out_gg:  assert (gg);  return *gg;
+        case token_type::out_ggg: assert (ggg); return *ggg;
+        }
+
+        return t;
+      }
+    };
+
+    class lexer: public build2::lexer
+    {
+    public:
+      using base_lexer = build2::lexer;
+      using base_mode = build2::lexer_mode;
+
+      using redirect_aliases_type = script::redirect_aliases;
+
+      // Note that none of the name, redirect aliases, and escape arguments
+      // are copied.
+      //
+      lexer (istream& is,
+             const path_name& name,
+             lexer_mode m,
+             const redirect_aliases_type& ra,
+             const char* escapes = nullptr)
+          : base_lexer (is, name, 1 /* line */,
+                        nullptr     /* escapes */,
+                        false       /* set_mode */),
+            redirect_aliases (ra)
+      {
+        mode (m, '\0', escapes);
+      }
+
+      virtual void
+      mode (base_mode,
+            char = '\0',
+            optional<const char*> = nullopt,
+            uintptr_t = 0) override;
+
+      // Number of quoted (double or single) tokens since last reset.
+      //
+      size_t
+      quoted () const {return quoted_;}
+
+      void
+      reset_quoted (size_t q) {quoted_ = q;}
+
+      virtual token
+      next () override;
+
+    public:
+      const redirect_aliases_type& redirect_aliases;
+
+    protected:
+      lexer (istream& is, const path_name& name, uint64_t line,
+             const char* escapes,
+             bool set_mode,
+             const redirect_aliases_type& ra)
+          : base_lexer (is, name, line, escapes, set_mode),
+            redirect_aliases (ra) {}
+
+      // Return the next token if it is a command operator (|, ||, &&,
+      // redirect, or cleanup) and nullopt otherwise.
+      //
+      optional<token>
+      next_cmd_op (const xchar&, // The token first character (last got char).
+                   bool sep);    // The token is separated.
+
+    private:
+      token
+      next_line ();
+
+    protected:
+      size_t quoted_;
+    };
+  }
+}
+
+#endif // LIBBUILD2_SCRIPT_LEXER_HXX
diff --git a/libbuild2/script/lexer.test.cxx b/libbuild2/script/lexer.test.cxx
new file mode 100644
index 0000000..b8de241
--- /dev/null
+++ b/libbuild2/script/lexer.test.cxx
@@ -0,0 +1,76 @@
+// file      : libbuild2/script/lexer.test.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <cassert>
+#include <iostream>
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/script/token.hxx>
+#include <libbuild2/script/lexer.hxx>
+
+using namespace std;
+
+namespace build2
+{
+  namespace script
+  {
+    // Usage: argv[0] <lexer-mode>
+    //
+    int
+    main (int argc, char* argv[])
+    {
+      lexer_mode m;
+      {
+        assert (argc == 2);
+        string s (argv[1]);
+
+        if      (s == "command-expansion") m = lexer_mode::command_expansion;
+        else if (s == "here-line-single")  m = lexer_mode::here_line_single;
+        else if (s == "here-line-double")  m = lexer_mode::here_line_double;
+        else                               assert (false);
+      }
+
+      try
+      {
+        cin.exceptions (istream::failbit | istream::badbit);
+
+        path_name in ("<stdin>");
+
+        using type = token_type;
+
+        redirect_aliases ra {type (type::in_file),
+                             type (type::in_doc),
+                             type (type::in_str),
+                             type (type::out_file_ovr),
+                             type (type::out_file_app),
+                             nullopt};
+
+        lexer l (cin, in, m, ra);
+
+        // No use printing eos since we will either get it or loop forever.
+        //
+        for (token t (l.next ()); t.type != token_type::eos; t = l.next ())
+        {
+          // Print each token on a separate line without quoting operators.
+          //
+          t.printer (cout, t, print_mode::normal);
+          cout << endl;
+        }
+      }
+      catch (const failed&)
+      {
+        return 1;
+      }
+
+      return 0;
+    }
+  }
+}
+
+int
+main (int argc, char* argv[])
+{
+  return build2::script::main (argc, argv);
+}
diff --git a/libbuild2/script/parser.cxx b/libbuild2/script/parser.cxx
new file mode 100644
index 0000000..aa60111
--- /dev/null
+++ b/libbuild2/script/parser.cxx
@@ -0,0 +1,2015 @@
+// file      : libbuild2/script/parser.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/script/parser.hxx>
+
+#include <libbuild2/variable.hxx>
+#include <libbuild2/script/run.hxx>   // exit
+#include <libbuild2/script/lexer.hxx>
+
+using namespace std;
+
+namespace build2
+{
+  namespace script
+  {
+    using type = token_type;
+
+    value parser::
+    parse_variable_line (token& t, type& tt)
+    {
+      // enter: assignment
+      // leave: newline or unknown token
+
+      next_with_attributes (t, tt);
+
+      // Parse value attributes if any. Note that it's ok not to have
+      // anything after the attributes (e.g., foo=[null]).
+      //
+      attributes_push (t, tt, true);
+
+      // @@ PAT: Should we expand patterns? Note that it will only be
+      // simple ones since we have disabled {}. Also, what would be the
+      // pattern base directory?
+      //
+      return tt != type::newline && start_names (tt)
+        ? parse_value (t, tt,
+                       pattern_mode::ignore,
+                       "variable value",
+                       nullptr)
+        : value (names ());
+    }
+
+    // Parse the regular expression representation (non-empty string value
+    // framed with introducer characters and optionally followed by flag
+    // characters from the {di} set, for example '/foo/id') into
+    // components. Also return end-of-parsing position if requested,
+    // otherwise treat any unparsed characters left as an error.
+    //
+    struct regex_parts
+    {
+      string value;
+      char   intro;
+      string flags; // Combination of characters from {di} set.
+
+      // Create a special empty object.
+      //
+      regex_parts (): intro ('\0') {}
+
+      regex_parts (string v, char i, string f)
+          : value (move (v)), intro (i), flags (move (f)) {}
+    };
+
+    static regex_parts
+    parse_regex (const string& s,
+                 const location& l,
+                 const char* what,
+                 size_t* end = nullptr)
+    {
+      if (s.empty ())
+        fail (l) << "no introducer character in " << what;
+
+      size_t p (s.find (s[0], 1)); // Find terminating introducer.
+
+      if (p == string::npos)
+        fail (l) << "no closing introducer character in " << what;
+
+      size_t rn (p - 1); // Regex length.
+      if (rn == 0)
+        fail (l) << what << " is empty";
+
+      // Find end-of-flags position.
+      //
+      size_t fp (++p); // Save flags starting position.
+      for (char c; (c = s[p]) == 'd' || c == 'i'; ++p) ;
+
+      // If string end is not reached then report invalid flags, unless
+      // end-of-parsing position is requested (which means regex is just a
+      // prefix).
+      //
+      if (s[p] != '\0' && end == nullptr)
+        fail (l) << "junk at the end of " << what;
+
+      if (end != nullptr)
+        *end = p;
+
+      return regex_parts (string (s, 1, rn), s[0], string (s, fp, p - fp));
+    }
+
+    pair<command_expr, parser::here_docs> parser::
+    parse_command_expr (token& t, type& tt,
+                        const redirect_aliases& ra)
+    {
+      // enter: first token of the command line
+      // leave: <newline> or unknown token
+
+      command_expr expr;
+
+      // OR-ed to an implied false for the first term.
+      //
+      expr.push_back ({expr_operator::log_or, command_pipe ()});
+
+      command c; // Command being assembled.
+
+      // Make sure the command makes sense.
+      //
+      auto check_command = [&c, this] (const location& l, bool last)
+      {
+        if (c.out && c.out->type == redirect_type::merge &&
+            c.err && c.err->type == redirect_type::merge)
+          fail (l) << "stdout and stderr redirected to each other";
+
+        if (!last && c.out)
+          fail (l) << "stdout is both redirected and piped";
+      };
+
+      // Check that the introducer character differs from '/' if the
+      // portable path modifier is specified. Must be called before
+      // parse_regex() (see below) to make sure its diagnostics is
+      // meaningful.
+      //
+      // Note that the portable path modifier assumes '/' to be a valid
+      // regex character and so makes it indistinguishable from the
+      // terminating introducer.
+      //
+      auto check_regex_mod = [this] (const string& mod,
+                                     const string& re,
+                                     const location& l,
+                                     const char* what)
+      {
+        // Handles empty regex properly.
+        //
+        if (mod.find ('/') != string::npos && re[0] == '/')
+          fail (l) << "portable path modifier and '/' introducer in "
+                   << what;
+      };
+
+      // Pending positions where the next word should go.
+      //
+      enum class pending
+      {
+        none,
+        program,
+        in_string,
+        in_document,
+        in_file,
+        out_merge,
+        out_string,
+        out_str_regex,
+        out_document,
+        out_doc_regex,
+        out_file,
+        err_merge,
+        err_string,
+        err_str_regex,
+        err_document,
+        err_doc_regex,
+        err_file,
+        clean
+      };
+      pending p (pending::program);
+      string mod;   // Modifiers for pending in_* and out_* positions.
+      here_docs hd; // Expected here-documents.
+
+      // Add the next word to either one of the pending positions or to
+      // program arguments by default.
+      //
+      auto add_word = [&c, &p, &mod, &check_regex_mod, this] (
+        string&& w, const location& l)
+      {
+        auto add_merge = [&l, this] (optional<redirect>& r,
+                                     const string& w,
+                                     int fd)
+        {
+          assert (r); // Must already be present.
+
+          try
+          {
+            size_t n;
+            if (stoi (w, &n) == fd && n == w.size ())
+            {
+              r->fd = fd;
+              return;
+            }
+          }
+          catch (const exception&) {} // Fall through.
+
+          fail (l) << (fd == 1 ? "stderr" : "stdout") << " merge redirect "
+                   << "file descriptor must be " << fd;
+        };
+
+        auto add_here_str = [] (optional<redirect>& r, string&& w)
+        {
+          assert (r); // Must already be present.
+
+          if (r->modifiers ().find (':') == string::npos)
+            w += '\n';
+          r->str = move (w);
+        };
+
+        auto add_here_str_regex = [&l, &check_regex_mod] (
+          optional<redirect>& r, int fd, string&& w)
+        {
+          assert (r); // Must already be present.
+
+          const char* what (nullptr);
+          switch (fd)
+          {
+          case 1: what = "stdout regex redirect"; break;
+          case 2: what = "stderr regex redirect"; break;
+          }
+
+          check_regex_mod (r->modifiers (), w, l, what);
+
+          regex_parts rp (parse_regex (w, l, what));
+
+          regex_lines& re (r->regex);
+          re.intro = rp.intro;
+
+          re.lines.emplace_back (
+            l.line, l.column, move (rp.value), move (rp.flags));
+
+          // Add final blank line unless suppressed.
+          //
+          // Note that the position is synthetic, but that's ok as we don't
+          // expect any diagnostics to refer this line.
+          //
+          if (r->modifiers ().find (':') == string::npos)
+            re.lines.emplace_back (l.line, l.column, string (), false);
+        };
+
+        auto parse_path = [&l, this] (string&& w, const char* what) -> path
+        {
+          try
+          {
+            path p (move (w));
+
+            if (!p.empty ())
+            {
+              p.normalize ();
+              return p;
+            }
+
+            fail (l) << "empty " << what << endf;
+          }
+          catch (const invalid_path& e)
+          {
+            fail (l) << "invalid " << what << " '" << e.path << "'" << endf;
+          }
+        };
+
+        auto add_file = [&parse_path] (optional<redirect>& r,
+                                       int fd,
+                                       string&& w)
+        {
+          assert (r); // Must already be present.
+
+          const char* what (nullptr);
+          switch (fd)
+          {
+          case 0: what = "stdin redirect path";  break;
+          case 1: what = "stdout redirect path"; break;
+          case 2: what = "stderr redirect path"; break;
+          }
+
+          r->file.path = parse_path (move (w), what);
+        };
+
+        switch (p)
+        {
+        case pending::none: c.arguments.push_back (move (w)); break;
+        case pending::program:
+          c.program = parse_path (move (w), "program path");
+          break;
+
+        case pending::out_merge: add_merge (c.out, w, 2); break;
+        case pending::err_merge: add_merge (c.err, w, 1); break;
+
+        case pending::in_string:  add_here_str (c.in,  move (w)); break;
+        case pending::out_string: add_here_str (c.out, move (w)); break;
+        case pending::err_string: add_here_str (c.err, move (w)); break;
+
+        case pending::out_str_regex:
+          {
+            add_here_str_regex (c.out, 1, move (w));
+            break;
+          }
+        case pending::err_str_regex:
+          {
+            add_here_str_regex (c.err, 2, move (w));
+            break;
+          }
+
+          // These are handled specially below.
+          //
+        case pending::in_document:
+        case pending::out_document:
+        case pending::err_document:
+        case pending::out_doc_regex:
+        case pending::err_doc_regex: assert (false); break;
+
+        case pending::in_file:  add_file (c.in,  0, move (w)); break;
+        case pending::out_file: add_file (c.out, 1, move (w)); break;
+        case pending::err_file: add_file (c.err, 2, move (w)); break;
+
+        case pending::clean:
+          {
+            cleanup_type t;
+            switch (mod[0]) // Ok, if empty
+            {
+            case '!': t = cleanup_type::never;  break;
+            case '?': t = cleanup_type::maybe;  break;
+            default:  t = cleanup_type::always; break;
+            }
+
+            c.cleanups.push_back (
+              {t, parse_path (move (w), "cleanup path")});
+            break;
+          }
+        }
+
+        p = pending::none;
+        mod.clear ();
+      };
+
+      // Make sure we don't have any pending positions to fill.
+      //
+      auto check_pending = [&p, this] (const location& l)
+      {
+        const char* what (nullptr);
+
+        switch (p)
+        {
+        case pending::none:                                            break;
+        case pending::program:      what = "program";                  break;
+        case pending::in_string:    what = "stdin here-string";        break;
+        case pending::in_document:  what = "stdin here-document end";  break;
+        case pending::in_file:      what = "stdin file";               break;
+        case pending::out_merge:    what = "stdout file descriptor";   break;
+        case pending::out_string:   what = "stdout here-string";       break;
+        case pending::out_document: what = "stdout here-document end"; break;
+        case pending::out_file:     what = "stdout file";              break;
+        case pending::err_merge:    what = "stderr file descriptor";   break;
+        case pending::err_string:   what = "stderr here-string";       break;
+        case pending::err_document: what = "stderr here-document end"; break;
+        case pending::err_file:     what = "stderr file";              break;
+        case pending::clean:        what = "cleanup path";             break;
+
+        case pending::out_str_regex:
+          {
+            what = "stdout here-string regex";
+            break;
+          }
+        case pending::err_str_regex:
+          {
+            what = "stderr here-string regex";
+            break;
+          }
+        case pending::out_doc_regex:
+          {
+            what = "stdout here-document regex end";
+            break;
+          }
+        case pending::err_doc_regex:
+          {
+            what = "stderr here-document regex end";
+            break;
+          }
+        }
+
+        if (what != nullptr)
+          fail (l) << "missing " << what;
+      };
+
+      // Parse the redirect operator.
+      //
+      // If the token type is the redirect alias then tt must contain the type
+      // the alias resolves to and the token type otherwise. Note that this
+      // argument defines the redirect semantics. Also note that the token is
+      // saved into the redirect to keep the modifiers and the original
+      // representation.
+      //
+      auto parse_redirect = [&c, &expr, &p, &mod, &hd, this]
+                            (token&& t, type tt, const location& l)
+      {
+        // The redirect alias token type must be resolved.
+        //
+        assert (tt != type::in_l   &&
+                tt != type::in_ll  &&
+                tt != type::in_lll &&
+                tt != type::out_g  &&
+                tt != type::out_gg &&
+                tt != type::out_ggg);
+
+        // Our semantics is the last redirect seen takes effect.
+        //
+        assert (p == pending::none && mod.empty ());
+
+        // See if we have the file descriptor.
+        //
+        unsigned long fd (3);
+        if (!t.separated)
+        {
+          if (c.arguments.empty ())
+            fail (l) << "missing redirect file descriptor";
+
+          const string& s (c.arguments.back ());
+
+          try
+          {
+            size_t n;
+            fd = stoul (s, &n);
+
+            if (n != s.size () || fd > 2)
+              throw invalid_argument (string ());
+          }
+          catch (const exception&)
+          {
+            fail (l) << "invalid redirect file descriptor '" << s << "'";
+          }
+
+          c.arguments.pop_back ();
+        }
+
+        // Validate/set default file descriptor.
+        //
+        switch (tt)
+        {
+        case type::in_pass:
+        case type::in_null:
+        case type::in_str:
+        case type::in_doc:
+        case type::in_file:
+          {
+            if ((fd = fd == 3 ? 0 : fd) != 0)
+              fail (l) << "invalid in redirect file descriptor " << fd;
+
+            if (!expr.back ().pipe.empty ())
+              fail (l) << "stdin is both piped and redirected";
+
+            break;
+          }
+        case type::out_pass:
+        case type::out_null:
+        case type::out_trace:
+        case type::out_merge:
+        case type::out_str:
+        case type::out_doc:
+        case type::out_file_cmp:
+        case type::out_file_ovr:
+        case type::out_file_app:
+          {
+            if ((fd = fd == 3 ? 1 : fd) == 0)
+              fail (l) << "invalid out redirect file descriptor " << fd;
+
+            break;
+          }
+        }
+
+        // Don't move as we will save the token into the redirect object.
+        //
+        mod = t.value;
+
+        // Handle the none redirect (no data allowed) in the switch construct
+        // if/when the respective syntax is invented.
+        //
+        redirect_type rt (redirect_type::none);
+        switch (tt)
+        {
+        case type::in_pass:
+        case type::out_pass:  rt = redirect_type::pass;  break;
+
+        case type::in_null:
+        case type::out_null:  rt = redirect_type::null;  break;
+
+        case type::out_trace: rt = redirect_type::trace; break;
+
+        case type::out_merge: rt = redirect_type::merge; break;
+
+        case type::in_str:
+        case type::out_str:
+          {
+            bool re (mod.find ('~') != string::npos);
+            assert (tt == type::out_str || !re);
+
+            rt = re
+              ? redirect_type::here_str_regex
+              : redirect_type::here_str_literal;
+
+            break;
+          }
+
+        case type::in_doc:
+        case type::out_doc:
+          {
+            bool re (mod.find ('~') != string::npos);
+            assert (tt == type::out_doc || !re);
+
+            rt = re
+              ? redirect_type::here_doc_regex
+              : redirect_type::here_doc_literal;
+
+            break;
+          }
+
+        case type::in_file:
+        case type::out_file_cmp:
+        case type::out_file_ovr:
+        case type::out_file_app: rt = redirect_type::file; break;
+        }
+
+        optional<redirect>& r (fd == 0 ? c.in  :
+                               fd == 1 ? c.out :
+                                         c.err);
+
+        optional<redirect_type> overriden;
+
+        if (r)
+          overriden = r->type;
+
+        r = redirect (rt);
+
+        // Don't move as still may be used for pending here-document end
+        // marker processing.
+        //
+        r->token = move (t);
+
+        switch (rt)
+        {
+        case redirect_type::none:
+          // Remove the assertion if/when the none redirect syntax is
+          // invented.
+          //
+          assert (false);
+          // Fall through.
+        case redirect_type::pass:
+        case redirect_type::null:
+        case redirect_type::trace:
+          break;
+        case redirect_type::merge:
+          switch (fd)
+          {
+          case 0: assert (false);         break;
+          case 1: p = pending::out_merge; break;
+          case 2: p = pending::err_merge; break;
+          }
+          break;
+        case redirect_type::here_str_literal:
+          switch (fd)
+          {
+          case 0: p = pending::in_string;  break;
+          case 1: p = pending::out_string; break;
+          case 2: p = pending::err_string; break;
+          }
+          break;
+        case redirect_type::here_str_regex:
+          switch (fd)
+          {
+          case 0: assert (false);             break;
+          case 1: p = pending::out_str_regex; break;
+          case 2: p = pending::err_str_regex; break;
+          }
+          break;
+        case redirect_type::here_doc_literal:
+          switch (fd)
+          {
+          case 0: p = pending::in_document;  break;
+          case 1: p = pending::out_document; break;
+          case 2: p = pending::err_document; break;
+          }
+          break;
+        case redirect_type::here_doc_regex:
+          switch (fd)
+          {
+          case 0: assert (false);             break;
+          case 1: p = pending::out_doc_regex; break;
+          case 2: p = pending::err_doc_regex; break;
+          }
+          break;
+        case redirect_type::file:
+          switch (fd)
+          {
+          case 0: p = pending::in_file;  break;
+          case 1: p = pending::out_file; break;
+          case 2: p = pending::err_file; break;
+          }
+
+          // Also sets for stdin, but this is harmless.
+          //
+          r->file.mode = tt == type::out_file_ovr ? redirect_fmode::overwrite :
+                         tt == type::out_file_app ? redirect_fmode::append    :
+                                                    redirect_fmode::compare;
+
+          break;
+
+        case redirect_type::here_doc_ref: assert (false); break;
+        }
+
+        // If we are overriding a here-document, then remove the reference
+        // to this command redirect from the corresponding here_doc object.
+        //
+        if (!pre_parse_ &&
+            overriden &&
+            (*overriden == redirect_type::here_doc_literal ||
+             *overriden == redirect_type::here_doc_regex))
+        {
+          size_t e (expr.size () - 1);
+          size_t p (expr.back ().pipe.size ());
+          int    f (static_cast<int> (fd));
+
+          for (here_doc& d: hd)
+          {
+            small_vector<here_redirect, 2>& rs (d.redirects);
+
+            auto i (find_if (rs.begin (), rs.end (),
+                             [e, p, f] (const here_redirect& r)
+                             {
+                               return r.expr == e &&
+                                 r.pipe == p &&
+                                 r.fd   == f;
+                             }));
+
+            if (i != rs.end ())
+            {
+              rs.erase (i);
+              break;
+            }
+          }
+        }
+      };
+
+      // Set pending cleanup type.
+      //
+      auto parse_clean = [&p, &mod] (token& t)
+      {
+        p = pending::clean;
+        mod = move (t.value);
+      };
+
+      const location ll (get_location (t)); // Line location.
+
+      // Keep parsing chunks of the command line until we see one of the
+      // "terminators" (newline, exit status comparison, etc).
+      //
+      location l (ll);
+      names ns; // Reuse to reduce allocations.
+
+      for (bool done (false); !done; l = get_location (t))
+      {
+        tt = ra.resolve (tt);
+
+        switch (tt)
+        {
+        case type::newline:
+          {
+            done = true;
+            break;
+          }
+
+        case type::equal:
+        case type::not_equal:
+          {
+            if (!pre_parse_)
+              check_pending (l);
+
+            c.exit = parse_command_exit (t, tt);
+
+            // Only a limited set of things can appear after the exit status
+            // so we check this here.
+            //
+            switch (tt)
+            {
+            case type::newline:
+
+            case type::pipe:
+            case type::log_or:
+            case type::log_and:
+              break;
+
+            default:
+              {
+                // Bail out if this is one of the unknown/unexpected tokens.
+                //
+                done = true;
+                break;
+              }
+            }
+
+            break;
+          }
+
+        case type::pipe:
+        case type::log_or:
+        case type::log_and:
+
+        case type::in_pass:
+        case type::out_pass:
+
+        case type::in_null:
+        case type::out_null:
+
+        case type::out_trace:
+
+        case type::out_merge:
+
+        case type::in_str:
+        case type::in_doc:
+        case type::out_str:
+        case type::out_doc:
+
+        case type::in_file:
+        case type::out_file_cmp:
+        case type::out_file_ovr:
+        case type::out_file_app:
+
+        case type::clean:
+          {
+            if (pre_parse_)
+            {
+              // The only things we need to handle here are the here-document
+              // and here-document regex end markers since we need to know
+              // how many of them to pre-parse after the command.
+              //
+              switch (tt)
+              {
+              case type::in_doc:
+              case type::out_doc:
+                mod = move (t.value);
+
+                bool re (mod.find ('~') != string::npos);
+                const char* what (re
+                                  ? "here-document regex end marker"
+                                  : "here-document end marker");
+
+                // We require the end marker to be a literal, unquoted word.
+                // In particularm, we don't allow quoted because of cases
+                // like foo"$bar" (where we will see word 'foo').
+                //
+                next (t, tt);
+
+                // We require the end marker to be an unquoted or completely
+                // quoted word. The complete quoting becomes important for
+                // cases like foo"$bar" (where we will see word 'foo').
+                //
+                // For good measure we could have also required it to be
+                // separated from the following token, but out grammar
+                // allows one to write >>EOO;. The problematic sequence
+                // would be >>FOO$bar -- on reparse it will be expanded
+                // as a single word.
+                //
+                if (tt != type::word || t.value.empty ())
+                  fail (t) << "expected " << what;
+
+                peek ();
+                const token& p (peeked ());
+                if (!p.separated)
+                {
+                  switch (p.type)
+                  {
+                  case type::dollar:
+                  case type::lparen:
+                    fail (p) << what << " must be literal";
+                  }
+                }
+
+                quote_type qt (t.qtype);
+                switch (qt)
+                {
+                case quote_type::unquoted:
+                  qt = quote_type::single; // Treat as single-quoted.
+                  break;
+                case quote_type::single:
+                case quote_type::double_:
+                  if (t.qcomp)
+                    break;
+                  // Fall through.
+                case quote_type::mixed:
+                  fail (t) << "partially-quoted " << what;
+                }
+
+                regex_parts r;
+                string end (move (t.value));
+
+                if (re)
+                {
+                  check_regex_mod (mod, end, l, what);
+
+                  r = parse_regex (end, l, what);
+                  end = move (r.value); // The "cleared" end marker.
+                }
+
+                bool literal (qt == quote_type::single);
+                bool shared (false);
+
+                for (const auto& d: hd)
+                {
+                  if (d.end == end)
+                  {
+                    auto check = [&t, &end, &re, this] (bool c,
+                                                        const char* what)
+                    {
+                      if (!c)
+                        fail (t) << "different " << what
+                                 << " for shared here-document "
+                                 << (re ? "regex '" : "'") << end << "'";
+                    };
+
+                    check (d.modifiers == mod, "modifiers");
+                    check (d.literal == literal, "quoting");
+
+                    if (re)
+                    {
+                      check (d.regex == r.intro, "introducers");
+                      check (d.regex_flags == r.flags, "global flags");
+                    }
+
+                    shared = true;
+                    break;
+                  }
+                }
+
+                if (!shared)
+                  hd.push_back (
+                    here_doc {
+                      {},
+                      move (end),
+                      literal,
+                      move (mod),
+                      r.intro, move (r.flags)});
+
+                break;
+              }
+
+              next (t, tt);
+              break;
+            }
+
+            // If this is one of the operators/separators, check that we
+            // don't have any pending locations to be filled.
+            //
+            check_pending (l);
+
+            // Note: there is another one in the inner loop below.
+            //
+            switch (tt)
+            {
+            case type::pipe:
+            case type::log_or:
+            case type::log_and:
+              {
+                // Check that the previous command makes sense.
+                //
+                check_command (l, tt != type::pipe);
+                expr.back ().pipe.push_back (move (c));
+
+                c = command ();
+                p = pending::program;
+
+                if (tt != type::pipe)
+                {
+                  expr_operator o (tt == type::log_or
+                                   ? expr_operator::log_or
+                                   : expr_operator::log_and);
+                  expr.push_back ({o, command_pipe ()});
+                }
+
+                break;
+              }
+
+            case type::in_pass:
+            case type::out_pass:
+
+            case type::in_null:
+            case type::out_null:
+
+            case type::out_trace:
+
+            case type::out_merge:
+
+            case type::in_str:
+            case type::in_doc:
+            case type::out_str:
+            case type::out_doc:
+
+            case type::in_file:
+            case type::out_file_cmp:
+            case type::out_file_ovr:
+            case type::out_file_app:
+              {
+                parse_redirect (move (t), tt, l);
+                break;
+              }
+
+            case type::clean:
+              {
+                parse_clean (t);
+                break;
+              }
+
+            default: assert (false); break;
+            }
+
+            next (t, tt);
+            break;
+          }
+        default:
+          {
+            // Bail out if this is one of the unknown tokens.
+            //
+            if (!start_names (tt))
+            {
+              done = true;
+              break;
+            }
+
+            // Here-document end markers are literal (we verified that above
+            // during pre-parsing) and we need to know whether they were
+            // quoted. So handle this case specially.
+            //
+            {
+              int fd;
+              switch (p)
+              {
+              case pending::in_document:   fd =  0; break;
+              case pending::out_document:
+              case pending::out_doc_regex: fd =  1; break;
+              case pending::err_document:
+              case pending::err_doc_regex: fd =  2; break;
+              default:                     fd = -1; break;
+              }
+
+              if (fd != -1)
+              {
+                if (tt != type::word || t.value.empty ())
+                  fail (t) << "expected here-document end marker";
+
+                here_redirect rd {
+                  expr.size () - 1, expr.back ().pipe.size (), fd};
+
+                string end (move (t.value));
+
+                regex_parts r;
+
+                if (p == pending::out_doc_regex ||
+                    p == pending::err_doc_regex)
+                {
+                  // We can't fail here as we already parsed all the end
+                  // markers during pre-parsing stage, and so no need in the
+                  // description.
+                  //
+                  r = parse_regex (end, l, "");
+                  end = move (r.value); // The "cleared" end marker.
+                }
+
+                bool shared (false);
+                for (auto& d: hd)
+                {
+                  // No need to check that redirects that share here-document
+                  // have the same modifiers, etc. That have been done during
+                  // pre-parsing.
+                  //
+                  if (d.end == end)
+                  {
+                    d.redirects.emplace_back (rd);
+                    shared = true;
+                    break;
+                  }
+                }
+
+                if (!shared)
+                  hd.push_back (
+                    here_doc {
+                      {rd},
+                        move (end),
+                          (t.qtype == quote_type::unquoted ||
+                           t.qtype == quote_type::single),
+                          move (mod),
+                          r.intro, move (r.flags)});
+
+                p = pending::none;
+                mod.clear ();
+
+                next (t, tt);
+                break;
+              }
+            }
+
+            // Parse the next chunk as simple names to get expansion, etc.
+            // Note that we do it in the chunking mode to detect whether
+            // anything in each chunk is quoted.
+            //
+            // @@ PAT: should we support pattern expansion? This is even
+            // fuzzier than the variable case above. Though this is the
+            // shell semantics. Think what happens when we do rm *.txt?
+            //
+            reset_quoted (t);
+            parse_names (t, tt,
+                         ns,
+                         pattern_mode::ignore,
+                         true,
+                         "command line",
+                         nullptr);
+
+            if (pre_parse_) // Nothing else to do if we are pre-parsing.
+              break;
+
+            // Process what we got. Determine whether anything inside was
+            // quoted (note that the current token is "next" and is not part
+            // of this).
+            //
+            bool q ((quoted () -
+                     (t.qtype != quote_type::unquoted ? 1 : 0)) != 0);
+
+            for (name& n: ns)
+            {
+              string s;
+
+              try
+              {
+                s = value_traits<string>::convert (move (n), nullptr);
+              }
+              catch (const invalid_argument&)
+              {
+                diag_record dr (fail (l));
+                dr << "invalid string value ";
+                to_stream (dr.os, n, true); // Quote.
+              }
+
+              // If it is a quoted chunk, then we add the word as is.
+              // Otherwise we re-lex it. But if the word doesn't contain any
+              // interesting characters (operators plus quotes/escapes),
+              // then no need to re-lex.
+              //
+              // NOTE: update quoting (script.cxx:to_stream_q()) if adding
+              // any new characters.
+              //
+              if (q || s.find_first_of ("|&<>\'\"\\") == string::npos)
+                add_word (move (s), l);
+              else
+              {
+                // If the chunk re-parsing results in error, our diagnostics
+                // will look like this:
+                //
+                // <string>:1:4: error: stdout merge redirect file descriptor must be 2
+                //   script:2:5: info: while parsing string '1>&a'
+                //
+                auto df = make_diag_frame (
+                  [this, s, &l](const diag_record& dr)
+                  {
+                    dr << info (l) << "while parsing string '" << s << "'";
+                  });
+
+                // When re-lexing we do "effective escaping" and only for
+                // ['"\] (quotes plus the backslash itself). In particular,
+                // there is no way to escape redirects, operators, etc. The
+                // idea is to prefer quoting except for passing literal
+                // quotes, for example:
+                //
+                // args = \"&foo\"
+                // cmd $args               # cmd &foo
+                //
+                // args = 'x=\"foo bar\"'
+                // cmd $args               # cmd x="foo bar"
+                //
+                istringstream is (s);
+                path_name in ("<string>");
+                lexer lex (is, in,
+                           lexer_mode::command_expansion,
+                           ra,
+                           "\'\"\\");
+
+                // Treat the first "sub-token" as always separated from what
+                // we saw earlier.
+                //
+                // Note that this is not "our" token so we cannot do
+                // fail(t). Rather we should do fail(l).
+                //
+                token t (lex.next ());
+                location l (build2::get_location (t, in));
+                t.separated = true;
+
+                string w;
+                bool f (t.type == type::eos); // If the whole thing is empty.
+
+                for (; t.type != type::eos; t = lex.next ())
+                {
+                  type tt (ra.resolve (t.type));
+                  l = build2::get_location (t, in);
+
+                  // Re-lexing double-quotes will recognize $, ( inside as
+                  // tokens so we have to reverse them back. Since we don't
+                  // treat spaces as separators we can be sure we will get
+                  // it right.
+                  //
+                  switch (tt)
+                  {
+                  case type::dollar: w += '$'; continue;
+                  case type::lparen: w += '('; continue;
+                  }
+
+                  // Retire the current word. We need to distinguish between
+                  // empty and non-existent (e.g., > vs >"").
+                  //
+                  if (!w.empty () || f)
+                  {
+                    add_word (move (w), l);
+                    f = false;
+                  }
+
+                  if (tt == type::word)
+                  {
+                    w = move (t.value);
+                    f = true;
+                    continue;
+                  }
+
+                  // If this is one of the operators/separators, check that
+                  // we don't have any pending locations to be filled.
+                  //
+                  check_pending (l);
+
+                  // Note: there is another one in the outer loop above.
+                  //
+                  switch (tt)
+                  {
+                  case type::pipe:
+                  case type::log_or:
+                  case type::log_and:
+                    {
+                      // Check that the previous command makes sense.
+                      //
+                      check_command (l, tt != type::pipe);
+                      expr.back ().pipe.push_back (move (c));
+
+                      c = command ();
+                      p = pending::program;
+
+                      if (tt != type::pipe)
+                      {
+                        expr_operator o (tt == type::log_or
+                                         ? expr_operator::log_or
+                                         : expr_operator::log_and);
+                        expr.push_back ({o, command_pipe ()});
+                      }
+
+                      break;
+                    }
+
+                  case type::in_pass:
+                  case type::out_pass:
+
+                  case type::in_null:
+                  case type::out_null:
+
+                  case type::out_trace:
+
+                  case type::out_merge:
+
+                  case type::in_str:
+                  case type::out_str:
+
+                  case type::in_file:
+                  case type::out_file_cmp:
+                  case type::out_file_ovr:
+                  case type::out_file_app:
+                    {
+                      parse_redirect (move (t), tt, l);
+                      break;
+                    }
+
+                  case type::clean:
+                    {
+                      parse_clean (t);
+                      break;
+                    }
+
+                  case type::in_doc:
+                  case type::out_doc:
+                    {
+                      fail (l) << "here-document redirect in expansion";
+                      break;
+                    }
+                  }
+                }
+
+                // Don't forget the last word.
+                //
+                if (!w.empty () || f)
+                  add_word (move (w), l);
+              }
+            }
+
+            ns.clear ();
+            break;
+          }
+        }
+      }
+
+      if (!pre_parse_)
+      {
+        // Verify we don't have anything pending to be filled and the
+        // command makes sense.
+        //
+        check_pending (l);
+        check_command (l, true);
+
+        expr.back ().pipe.push_back (move (c));
+      }
+
+      return make_pair (move (expr), move (hd));
+    }
+
+    command_exit parser::
+    parse_command_exit (token& t, type& tt)
+    {
+      // enter: equal/not_equal
+      // leave: token after exit status (one parse_names() chunk)
+
+      exit_comparison comp (tt == type::equal
+                            ? exit_comparison::eq
+                            : exit_comparison::ne);
+
+      // The next chunk should be the exit status.
+      //
+      next (t, tt);
+      location l (get_location (t));
+      names ns (parse_names (t, tt,
+                             pattern_mode::ignore,
+                             true,
+                             "exit status",
+                             nullptr));
+      unsigned long es (256);
+
+      if (!pre_parse_)
+      {
+        try
+        {
+          if (ns.size () == 1 && ns[0].simple () && !ns[0].empty ())
+            es = stoul (ns[0].value);
+        }
+        catch (const exception&) {} // Fall through.
+
+        if (es > 255)
+        {
+          diag_record dr;
+
+          dr << fail (l) << "expected exit status instead of ";
+          to_stream (dr.os, ns, true); // Quote.
+
+          dr << info << "exit status is an unsigned integer less than 256";
+        }
+      }
+
+      return command_exit {comp, static_cast<uint8_t> (es)};
+    }
+
+    void parser::
+    parse_here_documents (token& t, type& tt,
+                          pair<command_expr, here_docs>& p)
+    {
+      // enter: newline
+      // leave: newline
+
+      // Parse here-document fragments in the order they were mentioned on
+      // the command line.
+      //
+      for (here_doc& h: p.second)
+      {
+        // Switch to the here-line mode which is like single/double-quoted
+        // string but recognized the newline as a separator.
+        //
+        mode (h.literal
+              ? lexer_mode::here_line_single
+              : lexer_mode::here_line_double);
+        next (t, tt);
+
+        parsed_doc v (
+          parse_here_document (t, tt, h.end, h.modifiers, h.regex));
+
+        // If all the here-document redirects are overridden, then we just
+        // drop the fragment.
+        //
+        if (!pre_parse_ && !h.redirects.empty ())
+        {
+          auto i (h.redirects.cbegin ());
+
+          command& c (p.first[i->expr].pipe[i->pipe]);
+
+          optional<redirect>& r (i->fd == 0 ? c.in  :
+                                 i->fd == 1 ? c.out :
+                                              c.err);
+
+          assert (r); // Must be present since it is referred.
+
+          if (v.re)
+          {
+            assert (r->type == redirect_type::here_doc_regex);
+
+            r->regex = move (v.regex);
+            r->regex.flags = move (h.regex_flags);
+          }
+          else
+          {
+            assert (r->type == redirect_type::here_doc_literal);
+
+            r->str = move (v.str);
+          }
+
+          r->end        = move (h.end);
+          r->end_line   = v.end_line;
+          r->end_column = v.end_column;
+
+          // Note that our references cannot be invalidated because the
+          // command_expr/command-pipe vectors already contain all their
+          // elements.
+          //
+          for (++i; i != h.redirects.cend (); ++i)
+          {
+            command& c (p.first[i->expr].pipe[i->pipe]);
+
+            optional<redirect>& ir (i->fd == 0 ? c.in  :
+                                    i->fd == 1 ? c.out :
+                                                 c.err);
+
+            // Must be present since it is referenced by here-doc.
+            //
+            assert (ir);
+
+            // Note: preserve the original representation.
+            //
+            ir = redirect (redirect_type::here_doc_ref, *r, move (ir->token));
+          }
+        }
+
+        expire_mode ();
+      }
+    }
+
+    parser::parsed_doc parser::
+    parse_here_document (token& t, type& tt,
+                         const string& em,
+                         const string& mod,
+                         char re)
+    {
+      // enter: first token on first line
+      // leave: newline (after end marker)
+
+      // String literal. Note that when decide if to terminate the previously
+      // added line with a newline, we need to distinguish a yet empty result
+      // and the one that has a single blank line added.
+      //
+      optional<string> rs;
+
+      regex_lines rre;
+
+      // Here-documents can be indented. The leading whitespaces of the end
+      // marker line (called strip prefix) determine the indentation. Every
+      // other line in the here-document should start with this prefix which
+      // is automatically stripped. The only exception is a blank line.
+      //
+      // The fact that the strip prefix is only known at the end, after
+      // seeing all the lines, is rather inconvenient. As a result, the way
+      // we implement this is a bit hackish (though there is also something
+      // elegant about it): at the end of the pre-parse stage we are going
+      // re-examine the sequence of tokens that comprise this here-document
+      // and "fix up" the first token of each line by stripping the prefix.
+      //
+      string sp;
+
+      // Remember the position of the first token in this here-document.
+      //
+      size_t ri (pre_parse_ ? replay_data_.size () - 1 : 0);
+
+      // We will use the location of the first token on the line for the
+      // regex diagnostics. At the end of the loop it will point to the
+      // beginning of the end marker.
+      //
+      location l;
+
+      while (tt != type::eos)
+      {
+        l = get_location (t);
+
+        // Check if this is the end marker. For starters, it should be a
+        // single, unquoted word followed by a newline.
+        //
+        if (tt == type::word &&
+            t.qtype == quote_type::unquoted &&
+            peek () == type::newline)
+        {
+          const string& v (t.value);
+
+          size_t vn (v.size ());
+          size_t en (em.size ());
+
+          // Then check that it ends with the end marker.
+          //
+          if (vn >= en && v.compare (vn - en, en, em) == 0)
+          {
+            // Now check that the prefix only contains whitespaces.
+            //
+            size_t n (vn - en);
+
+            if (v.find_first_not_of (" \t") >= n)
+            {
+              assert (pre_parse_ || n == 0); // Should have been stripped.
+
+              if (n != 0)
+                sp.assign (v, 0, n); // Save the strip prefix.
+
+              next (t, tt); // Get the newline.
+              break;
+            }
+          }
+        }
+
+        // Expand the line (can be blank).
+        //
+        // @@ PAT: one could argue that if we do it in variables, then we
+        // should do it here as well. Though feels bizarre.
+        //
+        names ns (tt != type::newline
+                  ? parse_names (t, tt,
+                                 pattern_mode::ignore,
+                                 false,
+                                 "here-document line",
+                                 nullptr)
+                  : names ());
+
+        if (!pre_parse_)
+        {
+          // What shall we do if the expansion results in multiple names?
+          // For, example if the line contains just the variable expansion
+          // and it is of type strings. Adding all the elements space-
+          // separated seems like the natural thing to do.
+          //
+          string s;
+          for (auto b (ns.begin ()), i (b); i != ns.end (); ++i)
+          {
+            string n;
+
+            try
+            {
+              n = value_traits<string>::convert (move (*i), nullptr);
+            }
+            catch (const invalid_argument&)
+            {
+              fail (l) << "invalid string value '" << *i << "'";
+            }
+
+            if (i == b)
+              s = move (n);
+            else
+            {
+              s += ' ';
+              s += n;
+            }
+          }
+
+          if (!re)
+          {
+            // Add newline after previous line.
+            //
+            if (rs)
+            {
+              *rs += '\n';
+              *rs += s;
+            }
+            else
+              rs = move (s);
+          }
+          else
+          {
+            // Due to expansion we can end up with multiple lines. If empty
+            // then will add a blank textual literal.
+            //
+            for (size_t p (0); p != string::npos; )
+            {
+              string ln;
+              size_t np (s.find ('\n', p));
+
+              if (np != string::npos)
+              {
+                ln = string (s, p, np - p);
+                p = np + 1;
+              }
+              else
+              {
+                ln = string (s, p);
+                p = np;
+              }
+
+              if (ln[0] != re) // Line doesn't start with regex introducer.
+              {
+                // This is a line-char literal (covers blank lines as well).
+                //
+                // Append textual literal.
+                //
+                rre.lines.emplace_back (l.line, l.column, move (ln), false);
+              }
+              else // Line starts with the regex introducer.
+              {
+                // This is a char-regex, or a sequence of line-regex syntax
+                // characters or both (in this specific order). So we will
+                // add regex (with optional special characters) or special
+                // literal.
+                //
+                size_t p (ln.find (re, 1));
+                if (p == string::npos)
+                {
+                  // No regex, just a sequence of syntax characters.
+                  //
+                  string spec (ln, 1);
+                  if (spec.empty ())
+                    fail (l) << "no syntax line characters";
+
+                  // Append special literal.
+                  //
+                  rre.lines.emplace_back (
+                    l.line, l.column, move (spec), true);
+                }
+                else
+                {
+                  // Regex (probably with syntax characters).
+                  //
+                  regex_parts re;
+
+                  // Empty regex is a special case repesenting a blank line.
+                  //
+                  if (p == 1)
+                    // Position to optional specal characters of an empty
+                    // regex.
+                    //
+                    ++p;
+                  else
+                    // Can't fail as all the pre-conditions verified
+                    // (non-empty with both introducers in place), so no
+                    // description required.
+                    //
+                    re = parse_regex (ln, l, "", &p);
+
+                  // Append regex with optional special characters.
+                  //
+                  rre.lines.emplace_back (l.line, l.column,
+                                          move (re.value), move (re.flags),
+                                          string (ln, p));
+                }
+              }
+            }
+          }
+        }
+
+        // We should expand the whole line at once so this would normally be
+        // a newline but can also be an end-of-stream.
+        //
+        if (tt == type::newline)
+          next (t, tt);
+        else
+          assert (tt == type::eos);
+      }
+
+      if (tt == type::eos)
+        fail (t) << "missing here-document end marker '" << em << "'";
+
+      if (pre_parse_)
+      {
+        // Strip the indentation prefix if there is one.
+        //
+        assert (replay_ == replay::save);
+
+        if (!sp.empty ())
+        {
+          size_t sn (sp.size ());
+
+          for (; ri != replay_data_.size (); ++ri)
+          {
+            token& rt (replay_data_[ri].token);
+
+            if (rt.type == type::newline) // Blank
+              continue;
+
+            if (rt.type != type::word || rt.value.compare (0, sn, sp) != 0)
+              fail (rt) << "unindented here-document line";
+
+            // If the word is equal to the strip prefix then we have to drop
+            // the token. Note that simply making it an empty word won't
+            // have the same semantics. For instance, it would trigger
+            // concatenated expansion.
+            //
+            if (rt.value.size () == sn)
+              replay_data_.erase (replay_data_.begin () + ri);
+            else
+            {
+              rt.value.erase (0, sn);
+              rt.column += sn;
+              ++ri;
+            }
+
+            // Skip until next newline.
+            //
+            for (; replay_data_[ri].token.type != type::newline; ++ri) ;
+          }
+        }
+      }
+      else
+      {
+        // Add final newline unless suppressed.
+        //
+        if (mod.find (':') == string::npos)
+        {
+          if (re)
+            // Note that the position is synthetic, but that's ok as we don't
+            // expect any diagnostics to refer this line.
+            //
+            rre.lines.emplace_back (l.line, l.column, string (), false);
+          else if (rs)
+            *rs += '\n';
+          else
+            rs = "\n";
+        }
+
+        // Finalize regex lines.
+        //
+        if (re)
+        {
+          // Empty regex matches nothing, so not of much use.
+          //
+          if (rre.lines.empty ())
+            fail (l) << "empty here-document regex";
+
+          rre.intro  = re;
+        }
+      }
+
+      return re
+        ? parsed_doc (move (rre), l.line, l.column)
+        : parsed_doc (rs ? move (*rs) : string (), l.line, l.column);
+    }
+
+    size_t parser::
+    quoted () const
+    {
+      size_t r (0);
+
+      if (replay_ != replay::play)
+        r = lexer_->quoted ();
+      else
+      {
+        // Examine tokens we have replayed since last reset.
+        //
+        for (size_t i (replay_quoted_); i != replay_i_; ++i)
+          if (replay_data_[i].token.qtype != quote_type::unquoted)
+            ++r;
+      }
+
+      return r;
+    }
+
+    void parser::
+    reset_quoted (token& cur)
+    {
+      if (replay_ != replay::play)
+        lexer_->reset_quoted (cur.qtype != quote_type::unquoted ? 1 : 0);
+      else
+      {
+        replay_quoted_ = replay_i_ - 1;
+
+        // Must be the same token.
+        //
+        assert (replay_data_[replay_quoted_].token.qtype == cur.qtype);
+      }
+    }
+
+    void parser::
+    set_lexer (lexer* l)
+    {
+      lexer_ = l;
+      build2::parser::lexer_ = l;
+    }
+
+    static redirect_aliases no_redirect_aliases;
+
+    void parser::
+    apply_value_attributes (const variable* var,
+                            value& lhs,
+                            value&& rhs,
+                            const string& attributes,
+                            token_type kind,
+                            const path_name& name)
+    {
+      path_ = &name;
+
+      istringstream is (attributes);
+
+      // Note that the redirect alias information is not used in the
+      // attributes lexer mode.
+      //
+      lexer l (is, name, lexer_mode::attributes, no_redirect_aliases);
+
+      set_lexer (&l);
+
+      token t;
+      type tt;
+
+      next_with_attributes (t, tt); // Enable `[` recognition.
+
+      if (tt != type::lsbrace && tt != type::eos)
+        fail (t) << "expected '[' instead of " << t;
+
+      attributes_push (t, tt, true);
+
+      if (tt != type::eos)
+        fail (t) << "trailing junk after ']'";
+
+      build2::parser::apply_value_attributes (var, lhs, move (rhs), kind);
+    }
+
+    line_type parser::
+    pre_parse_line_start (token& t, token_type& tt, lexer_mode stm)
+    {
+      replay_save (); // Start saving tokens from the current one.
+      next (t, tt);
+
+      // Decide whether this is a variable assignment or a command.
+      //
+      // It is an assignment if the first token is an unquoted name and
+      // the next token is an assign/append/prepend operator. Assignment
+      // to a computed variable name must use the set builtin.
+      //
+      // Note also that special commands take precedence over variable
+      // assignments.
+      //
+      line_type r (line_type::cmd); // Default.
+
+      if (tt == type::word && t.qtype == quote_type::unquoted)
+      {
+        const string& n (t.value);
+
+        if      (n == "if")    r = line_type::cmd_if;
+        else if (n == "if!")   r = line_type::cmd_ifn;
+        else if (n == "elif")  r = line_type::cmd_elif;
+        else if (n == "elif!") r = line_type::cmd_elifn;
+        else if (n == "else")  r = line_type::cmd_else;
+        else if (n == "end")   r = line_type::cmd_end;
+        else
+        {
+          // Switch the recognition of leading variable assignments for
+          // the next token. This is safe to do because we know we
+          // cannot be in the quoted mode (since the current token is
+          // not quoted).
+          //
+          type p (peek (stm));
+
+          if (p == type::assign  || p == type::prepend || p == type::append)
+          {
+            r = line_type::var;
+
+            // Note that the missing command program is detected later, by
+            // parse_command_expr().
+            //
+            if (n.empty ())
+              fail (t) << "missing variable name";
+          }
+        }
+      }
+
+      return r;
+    }
+
+    bool parser::
+    exec_lines (lines::const_iterator i, lines::const_iterator e,
+                const function<exec_set_function>& exec_set,
+                const function<exec_cmd_function>& exec_cmd,
+                const function<exec_if_function>& exec_if,
+                size_t& li,
+                variable_pool* var_pool)
+    {
+      try
+      {
+        token t;
+        type tt;
+        for (; i != e; ++i)
+        {
+          const line& ln (*i);
+          line_type lt (ln.type);
+
+          assert (path_ == nullptr);
+
+          // Copy the tokens and start playing.
+          //
+          replay_data (replay_tokens (ln.tokens));
+
+          // We don't really need to change the mode since we already know
+          // the line type.
+          //
+          next (t, tt);
+          const location ll (get_location (t));
+
+          switch (lt)
+          {
+          case line_type::var:
+            {
+              // Enter the variable into the pool if this is not done during
+              // the script parsing. Note that in this case the pool is
+              // expected to be provided.
+              //
+              const variable* var (ln.var);
+
+              if (var == nullptr)
+              {
+                assert (var_pool != nullptr);
+
+                var = &var_pool->insert (t.value);
+              }
+
+              exec_set (*var, t, tt, ll);
+
+              replay_stop ();
+              break;
+            }
+          case line_type::cmd:
+            {
+              bool single (false);
+
+              if (li == 1)
+              {
+                lines::const_iterator j (i);
+                for (++j; j != e && j->type == line_type::var; ++j) ;
+
+                if (j == e) // We have no another command.
+                  single = true;
+              }
+
+              exec_cmd (t, tt, li++, single, ll);
+
+              replay_stop ();
+              break;
+            }
+          case line_type::cmd_if:
+          case line_type::cmd_ifn:
+          case line_type::cmd_elif:
+          case line_type::cmd_elifn:
+          case line_type::cmd_else:
+            {
+              next (t, tt); // Skip to start of command.
+
+              bool take;
+              if (lt != line_type::cmd_else)
+              {
+                take = exec_if (t, tt, li++, ll);
+
+                if (lt == line_type::cmd_ifn || lt == line_type::cmd_elifn)
+                  take = !take;
+              }
+              else
+              {
+                assert (tt == type::newline);
+                take = true;
+              }
+
+              replay_stop ();
+
+              // If end is true, then find the 'end' line. Otherwise, find
+              // the next if-else line. If skip is true then increment the
+              // command line index.
+              //
+              auto next = [e, &li] (lines::const_iterator j,
+                                    bool end,
+                                    bool skip) -> lines::const_iterator
+                {
+                  // We need to be aware of nested if-else chains.
+                  //
+                  size_t n (0);
+
+                  for (++j; j != e; ++j)
+                  {
+                    line_type lt (j->type);
+
+                    if (lt == line_type::cmd_if || lt == line_type::cmd_ifn)
+                      ++n;
+
+                    // If we are nested then we just wait until we get back
+                    // to the surface.
+                    //
+                    if (n == 0)
+                    {
+                      switch (lt)
+                      {
+                      case line_type::cmd_elif:
+                      case line_type::cmd_elifn:
+                      case line_type::cmd_else:
+                        if (end) break;
+                        // Fall through.
+                      case line_type::cmd_end:  return j;
+                      default: break;
+                      }
+                    }
+
+                    if (lt == line_type::cmd_end)
+                      --n;
+
+                    if (skip)
+                    {
+                      // Note that we don't count else and end as commands.
+                      //
+                      switch (lt)
+                      {
+                      case line_type::cmd:
+                      case line_type::cmd_if:
+                      case line_type::cmd_ifn:
+                      case line_type::cmd_elif:
+                      case line_type::cmd_elifn: ++li; break;
+                      default:                         break;
+                      }
+                    }
+                  }
+
+                  assert (false); // Missing end.
+                  return e;
+                };
+
+              // If we are taking this branch then we need to parse all the
+              // lines until the next if-else line and then skip all the
+              // lines until the end (unless next is already end).
+              //
+              // Otherwise, we need to skip all the lines until the next
+              // if-else line and then continue parsing.
+              //
+              if (take)
+              {
+                // Next if-else.
+                //
+                lines::const_iterator j (next (i, false, false));
+                if (!exec_lines (i + 1, j,
+                                 exec_set, exec_cmd, exec_if,
+                                 li,
+                                 var_pool))
+                  return false;
+
+                i = j->type == line_type::cmd_end ? j : next (j, true, true);
+              }
+              else
+              {
+                i = next (i, false, true);
+                if (i->type != line_type::cmd_end)
+                  --i; // Continue with this line (e.g., elif or else).
+              }
+
+              break;
+            }
+          case line_type::cmd_end:
+            {
+              assert (false);
+            }
+          }
+        }
+
+        return true;
+      }
+      catch (const exit& e)
+      {
+        // Bail out if the script is exited with the failure status. Otherwise
+        // exit the lines execution normally.
+        //
+        if (!e.status)
+          throw failed ();
+
+        replay_stop ();
+        return false;
+      }
+    }
+
+    // parser::parsed_doc
+    //
+    parser::parsed_doc::
+    parsed_doc (string s, uint64_t l, uint64_t c)
+        : str (move (s)), re (false), end_line (l), end_column (c)
+    {
+    }
+
+    parser::parsed_doc::
+    parsed_doc (regex_lines&& r, uint64_t l, uint64_t c)
+        : regex (move (r)), re (true), end_line (l), end_column (c)
+    {
+    }
+
+    parser::parsed_doc::
+    parsed_doc (parsed_doc&& d)
+        : re (d.re), end_line (d.end_line), end_column (d.end_column)
+    {
+      if (re)
+        new (&regex) regex_lines (move (d.regex));
+      else
+        new (&str) string (move (d.str));
+    }
+
+    parser::parsed_doc::
+    ~parsed_doc ()
+    {
+      if (re)
+        regex.~regex_lines ();
+      else
+        str.~string ();
+    }
+  }
+}
diff --git a/libbuild2/script/parser.hxx b/libbuild2/script/parser.hxx
new file mode 100644
index 0000000..a63ecde
--- /dev/null
+++ b/libbuild2/script/parser.hxx
@@ -0,0 +1,189 @@
+// file      : libbuild2/script/parser.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_SCRIPT_PARSER_HXX
+#define LIBBUILD2_SCRIPT_PARSER_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/forward.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/parser.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/script/token.hxx>
+#include <libbuild2/script/lexer.hxx>  // redirect_aliases
+#include <libbuild2/script/script.hxx>
+
+namespace build2
+{
+  namespace script
+  {
+    class  lexer;
+    struct lexer_mode;
+
+    class parser: protected build2::parser
+    {
+    public:
+      parser (context& c): build2::parser (c) {}
+
+      // Helpers.
+      //
+      // Parse attribute string and perform attribute-guided assignment.
+      // Issue diagnostics and throw failed in case of an error.
+      //
+      void
+      apply_value_attributes (const variable*, // Optional.
+                              value& lhs,
+                              value&& rhs,
+                              const string& attributes,
+                              token_type assign_kind,
+                              const path_name&); // For diagnostics.
+
+      using build2::parser::apply_value_attributes;
+
+      // Commonly used parsing functions. Issue diagnostics and throw failed
+      // in case of an error.
+      //
+      // Usually (but not always) parse functions receive the token/type
+      // from which it should start consuming and in return the token/type
+      // should contain the first token that has not been consumed.
+      //
+      // Functions that are called parse_*() rather than pre_parse_*() can be
+      // used for both stages.
+      //
+    protected:
+      value
+      parse_variable_line (token&, token_type&);
+
+      // Ordered sequence of here-document redirects that we can expect to
+      // see after the command line.
+      //
+      struct here_redirect
+      {
+        size_t expr; // Index in command_expr.
+        size_t pipe; // Index in command_pipe.
+        int fd;      // Redirect fd (0 - in, 1 - out, 2 - err).
+      };
+
+      struct here_doc
+      {
+        // Redirects that share here_doc. Most of the time we will have no
+        // more than 2 (2 - for the roundtrip cases). Doesn't refer overridden
+        // redirects and thus can be empty.
+        //
+        small_vector<here_redirect, 2> redirects;
+
+        string end;
+        bool literal;     // Literal (single-quote).
+        string modifiers;
+
+        // Regex introducer ('\0' if not a regex, so can be used as bool).
+        //
+        char regex;
+
+        // Regex global flags. Meaningful if regex != '\0'.
+        //
+        string regex_flags;
+      };
+      using here_docs = vector<here_doc>;
+
+      pair<command_expr, here_docs>
+      parse_command_expr (token&, token_type&, const redirect_aliases&);
+
+      command_exit
+      parse_command_exit (token&, token_type&);
+
+      void
+      parse_here_documents (token&, token_type&,
+                            pair<command_expr, here_docs>&);
+
+      struct parsed_doc
+      {
+        union
+        {
+          string str;        // Here-document literal.
+          regex_lines regex; // Here-document regex.
+        };
+
+        bool re;             // True if regex.
+        uint64_t end_line;   // Here-document end marker location.
+        uint64_t end_column;
+
+        parsed_doc (string, uint64_t line, uint64_t column);
+        parsed_doc (regex_lines&&, uint64_t line, uint64_t column);
+        parsed_doc (parsed_doc&&); // Note: move constuctible-only type.
+        ~parsed_doc ();
+      };
+
+      parsed_doc
+      parse_here_document (token&, token_type&,
+                           const string&,
+                           const string& mode,
+                           char re_intro);      // '\0' if not a regex.
+
+      // Start pre-parsing a script line returning its type, detected based on
+      // the first two tokens. Use the specified lexer mode to peek the second
+      // token.
+      //
+      line_type
+      pre_parse_line_start (token&, token_type&, lexer_mode);
+
+      // Execute.
+      //
+    protected:
+      // Return false if the execution of the script should be terminated with
+      // the success status (e.g., as a result of encountering the exit
+      // builtin). For unsuccessful termination the failed exception is thrown.
+      //
+      using exec_set_function = void (const variable&,
+                                      token&, token_type&,
+                                      const location&);
+
+      using exec_cmd_function = void (token&, token_type&,
+                                      size_t li,
+                                      bool single,
+                                      const location&);
+
+      using exec_if_function  = bool (token&, token_type&,
+                                      size_t li,
+                                      const location&);
+
+      // If a parser implementation doesn't pre-enter variables into a pool
+      // during the pre-parsing phase, then they are entered during the
+      // execution phase and so the variable pool must be provided. Note that
+      // in this case the variable pool insertions are not MT-safe.
+      //
+      bool
+      exec_lines (lines::const_iterator b, lines::const_iterator e,
+                  const function<exec_set_function>&,
+                  const function<exec_cmd_function>&,
+                  const function<exec_if_function>&,
+                  size_t& li,
+                  variable_pool* = nullptr);
+
+      // Set lexer pointers for both the current and the base classes.
+      //
+    protected:
+      void
+      set_lexer (lexer*);
+
+      // Number of quoted tokens since last reset. Note that this includes
+      // the peeked token, if any.
+      //
+    protected:
+      size_t
+      quoted () const;
+
+      void
+      reset_quoted (token& current);
+
+      size_t replay_quoted_;
+
+    protected:
+      lexer* lexer_ = nullptr;
+    };
+  }
+}
+
+#endif // LIBBUILD2_SCRIPT_PARSER_HXX
diff --git a/libbuild2/script/regex.cxx b/libbuild2/script/regex.cxx
new file mode 100644
index 0000000..3f796b6
--- /dev/null
+++ b/libbuild2/script/regex.cxx
@@ -0,0 +1,436 @@
+// file      : libbuild2/script/regex.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <locale>
+
+#include <libbuild2/script/regex.hxx>
+
+using namespace std;
+
+namespace build2
+{
+  namespace script
+  {
+    namespace regex
+    {
+      static_assert (alignof (char_string) % 4 == 0,
+                     "unexpected char_string alignment");
+
+      static_assert (alignof (char_regex) % 4 == 0,
+                     "unexpected char_regex alignment");
+
+      static_assert (sizeof (uintptr_t) > sizeof (int16_t),
+                     "unexpected uintptr_t size");
+
+      const line_char line_char::nul (0);
+      const line_char line_char::eof (-1);
+
+      // line_char
+      //
+      // We package the special character into uintptr_t with the following
+      // steps:
+      //
+      // - narrow down int value to int16_t (preserves all the valid values)
+      //
+      // - convert to uint16_t (bitwise representation stays the same, but no
+      //   need to bother with signed value widening, leftmost bits loss on
+      //   left shift, etc)
+      //
+      // - convert to uintptr_t (storage type)
+      //
+      // - shift left by two bits (the operation is fully reversible as
+      //   uintptr_t is wider then uint16_t)
+      //
+      line_char::
+      line_char (int c)
+          : data_ (
+            (static_cast <uintptr_t> (
+              static_cast<uint16_t> (
+                static_cast<int16_t> (c))) << 2) |
+            static_cast <uintptr_t> (line_type::special))
+      {
+        // @@ How can we allow anything for basic_regex but only subset
+        //    for our own code?
+        //
+        const char ex[] = "pn\n\r";
+
+        assert (c == 0  || // Null character.
+
+                // EOF. Note that is also passed by msvcrt as _Meta_eos
+                // enum value.
+                //
+                c == -1 ||
+
+                // libstdc++ line/paragraph separators.
+                //
+                c == u'\u2028' || c == u'\u2029' ||
+
+                (c > 0 && c <= 255 && (
+                  // Supported regex special characters.
+                  //
+                  syntax (c) ||
+
+                  // libstdc++ look-ahead tokens, newline chars.
+                  //
+                  string::traits_type::find (ex, 4, c) != nullptr)));
+      }
+
+      line_char::
+      line_char (const char_string& s, line_pool& p)
+          : line_char (&(*p.strings.emplace (s).first))
+      {
+      }
+
+      line_char::
+      line_char (char_string&& s, line_pool& p)
+          : line_char (&(*p.strings.emplace (move (s)).first))
+      {
+      }
+
+      line_char::
+      line_char (char_regex r, line_pool& p)
+          // Note: in C++17 can write as p.regexes.emplace_front(move (r))
+          //
+          : line_char (&(*p.regexes.emplace (p.regexes.begin (), move (r))))
+      {
+      }
+
+      bool
+      line_char::syntax (char c)
+      {
+        return string::traits_type::find (
+          "()|.*+?{}\\0123456789,=!", 23, c) != nullptr;
+      }
+
+      bool
+      operator== (const line_char& l, const line_char& r)
+      {
+        line_type lt (l.type ());
+        line_type rt (r.type ());
+
+        if (lt == rt)
+        {
+          bool res (true);
+
+          switch (lt)
+          {
+          case line_type::special: res = l.special () == r.special (); break;
+          case line_type::regex:   assert (false); break;
+
+            // Note that we use pointers (rather than vales) comparison
+            // assuming that the strings must belong to the same pool.
+            //
+          case line_type::literal: res = l.literal () == r.literal (); break;
+          }
+
+          return res;
+        }
+
+        // Match literal with regex.
+        //
+        if (lt == line_type::literal && rt == line_type::regex)
+          return regex_match (*l.literal (), *r.regex ());
+        else if (rt == line_type::literal && lt == line_type::regex)
+          return regex_match (*r.literal (), *l.regex ());
+
+        return false;
+      }
+
+      bool
+      operator< (const line_char& l, const line_char& r)
+      {
+        if (l == r)
+          return false;
+
+        line_type lt (l.type ());
+        line_type rt (r.type ());
+
+        if (lt != rt)
+          return lt < rt;
+
+        bool res (false);
+
+        switch (lt)
+        {
+        case line_type::special: res =  l.special () <  r.special (); break;
+        case line_type::literal: res = *l.literal () < *r.literal (); break;
+        case line_type::regex:   assert (false); break;
+        }
+
+        return res;
+      }
+
+      // line_char_locale
+      //
+
+      // An exemplar locale with the std::ctype<line_char> facet. It is used
+      // for the subsequent line char locale objects creation (see below)
+      // which normally ends up with a shallow copy of a reference-counted
+      // object.
+      //
+      // Note that creating the line char locales from the exemplar is not
+      // merely an optimization: there is a data race in the libstdc++ (at
+      // least as of GCC 9.1) implementation of the locale(const locale&,
+      // Facet*) constructor (bug #91057).
+      //
+      // Also note that we install the facet in init() rather than during
+      // the object creation to avoid a race with the std::locale-related
+      // global variables initialization.
+      //
+      static locale line_char_locale_exemplar;
+
+      void
+      init ()
+      {
+        line_char_locale_exemplar =
+          locale (locale (),
+                  new std::ctype<line_char> ()); // Hidden by ctype bitmask.
+      }
+
+      line_char_locale::
+      line_char_locale ()
+          : locale (line_char_locale_exemplar)
+      {
+        // Make sure init() has been called.
+        //
+        // Note: has_facet() is hidden by a private function in libc++.
+        //
+        assert (std::has_facet<std::ctype<line_char>> (*this));
+      }
+
+      // char_regex
+      //
+      // Transform regex according to the extended flags {idot}. If regex is
+      // malformed then keep transforming, so the resulting string is
+      // malformed the same way. We expect the error to be reported by the
+      // char_regex ctor.
+      //
+      static string
+      transform (const string& s, char_flags f)
+      {
+        assert ((f & char_flags::idot) != char_flags::none);
+
+        string r;
+        bool escape (false);
+        bool cclass (false);
+
+        for (char c: s)
+        {
+          // Inverse escaping for a dot which is out of the char class
+          // brackets.
+          //
+          bool inverse (c == '.' && !cclass);
+
+          // Handle the escape case. Note that we delay adding the backslash
+          // since we may have to inverse things.
+          //
+          if (escape)
+          {
+            if (!inverse)
+              r += '\\';
+
+            r += c;
+            escape = false;
+
+            continue;
+          }
+          else if (c == '\\')
+          {
+            escape = true;
+            continue;
+          }
+
+          // Keep track of being inside the char class brackets, escape if
+          // inversion. Note that we never inverse square brackets.
+          //
+          if (c == '[' && !cclass)
+            cclass = true;
+          else if (c == ']' && cclass)
+            cclass = false;
+          else if (inverse)
+            r += '\\';
+
+          r += c;
+        }
+
+        if (escape) // Regex is malformed but that's not our problem.
+          r += '\\';
+
+        return r;
+      }
+
+      static char_regex::flag_type
+      to_std_flags (char_flags f)
+      {
+        // Note that ECMAScript flag is implied in the absense of a grammar
+        // flag.
+        //
+        return (f & char_flags::icase) != char_flags::none
+          ? char_regex::icase
+          : char_regex::flag_type ();
+      }
+
+      char_regex::
+      char_regex (const char_string& s, char_flags f)
+          : base_type ((f & char_flags::idot) != char_flags::none
+                       ? transform (s, f)
+                       : s,
+                       to_std_flags (f))
+      {
+      }
+    }
+  }
+}
+
+namespace std
+{
+  using namespace build2::script::regex;
+
+  // char_traits<line_char>
+  //
+  line_char* char_traits<line_char>::
+  assign (char_type* s, size_t n, char_type c)
+  {
+    for (size_t i (0); i != n; ++i)
+      s[i] = c;
+    return s;
+  }
+
+  line_char* char_traits<line_char>::
+  move (char_type* d, const char_type* s, size_t n)
+  {
+    if (n > 0 && d != s)
+    {
+      // If d < s then it can't be in [s, s + n) range and so using copy() is
+      // safe. Otherwise d + n is out of (s, s + n] range and so using
+      // copy_backward() is safe.
+      //
+      if (d < s)
+        std::copy (s, s + n, d); // Hidden by char_traits<line_char>::copy().
+      else
+        copy_backward (s, s + n, d + n);
+    }
+
+    return d;
+  }
+
+  line_char* char_traits<line_char>::
+  copy (char_type* d, const char_type* s, size_t n)
+  {
+    std::copy (s, s + n, d); // Hidden by char_traits<line_char>::copy().
+    return d;
+  }
+
+  int char_traits<line_char>::
+  compare (const char_type* s1, const char_type* s2, size_t n)
+  {
+    for (size_t i (0); i != n; ++i)
+    {
+      if (s1[i] < s2[i])
+        return -1;
+      else if (s2[i] < s1[i])
+        return 1;
+    }
+
+    return 0;
+  }
+
+  size_t char_traits<line_char>::
+  length (const char_type* s)
+  {
+    size_t i (0);
+    while (s[i] != char_type::nul)
+      ++i;
+
+    return i;
+  }
+
+  const line_char* char_traits<line_char>::
+  find (const char_type* s, size_t n, const char_type& c)
+  {
+    for (size_t i (0); i != n; ++i)
+    {
+      if (s[i] == c)
+        return s + i;
+    }
+
+    return nullptr;
+  }
+
+  // ctype<line_char>
+  //
+  locale::id ctype<line_char>::id;
+
+  const line_char* ctype<line_char>::
+  is (const char_type* b, const char_type* e, mask* m) const
+  {
+    while (b != e)
+    {
+      const char_type& c (*b++);
+
+      *m++ = c.type () == line_type::special && c.special () >= 0 &&
+        build2::digit (static_cast<char> (c.special ()))
+        ? digit
+        : 0;
+    }
+
+    return e;
+  }
+
+  const line_char* ctype<line_char>::
+  scan_is (mask m, const char_type* b, const char_type* e) const
+  {
+    for (; b != e; ++b)
+    {
+      if (is (m, *b))
+        return b;
+    }
+
+    return e;
+  }
+
+  const line_char* ctype<line_char>::
+  scan_not (mask m, const char_type* b, const char_type* e) const
+  {
+    for (; b != e; ++b)
+    {
+      if (!is (m, *b))
+        return b;
+    }
+
+    return e;
+  }
+
+  const char* ctype<line_char>::
+  widen (const char* b, const char* e, char_type* c) const
+  {
+    while (b != e)
+      *c++ = widen (*b++);
+
+    return e;
+  }
+
+  const line_char* ctype<line_char>::
+  narrow (const char_type* b, const char_type* e, char def, char* c) const
+  {
+    while (b != e)
+      *c++ = narrow (*b++, def);
+
+    return e;
+  }
+
+  // regex_traits<line_char>
+  //
+  int regex_traits<line_char>::
+  value (char_type c, int radix) const
+  {
+    assert (radix == 8 || radix == 10 || radix == 16);
+
+    if (c.type () != line_type::special)
+      return -1;
+
+    const char digits[] = "0123456789ABCDEF";
+    const char* d (string::traits_type::find (digits, radix, c.special ()));
+    return d != nullptr ? static_cast<int> (d - digits) : -1;
+  }
+}
diff --git a/libbuild2/script/regex.hxx b/libbuild2/script/regex.hxx
new file mode 100644
index 0000000..30d3363
--- /dev/null
+++ b/libbuild2/script/regex.hxx
@@ -0,0 +1,678 @@
+// file      : libbuild2/script/regex.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_SCRIPT_REGEX_HXX
+#define LIBBUILD2_SCRIPT_REGEX_HXX
+
+#include <list>
+#include <regex>
+#include <locale>
+#include <string>        // basic_string
+#include <type_traits>   // make_unsigned, enable_if, is_*
+#include <unordered_set>
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+namespace build2
+{
+  namespace script
+  {
+    namespace regex
+    {
+      using char_string = std::basic_string<char>;
+
+      enum class char_flags: uint16_t
+      {
+        icase = 0x1, // Case-insensitive match.
+          idot  = 0x2, // Invert '.' escaping.
+
+          none = 0
+          };
+
+      // Restricts valid standard flags to just {icase}, extends with custom
+      // flags {idot}.
+      //
+      class char_regex: public std::basic_regex<char>
+      {
+      public:
+        using base_type = std::basic_regex<char>;
+
+        char_regex (const char_string&, char_flags = char_flags::none);
+      };
+
+      // Newlines are line separators and are not part of the line:
+      //
+      // line<newline>line<newline>
+      //
+      // Specifically, this means that a customary trailing newline creates a
+      // trailing blank line.
+      //
+      // All characters can inter-compare (though there cannot be regex
+      // characters in the output, only in line_regex).
+      //
+      // Note that we assume that line_regex and the input to regex_match()
+      // use the same pool.
+      //
+      struct line_pool
+      {
+        // Note that we assume the pool can be moved without invalidating
+        // pointers to any already pooled entities.
+        //
+        std::unordered_set<char_string> strings;
+        std::list<char_regex> regexes;
+      };
+
+      enum class line_type
+      {
+        special,
+          literal,
+          regex
+          };
+
+      struct line_char
+      {
+        // Steal last two bits from the pointer to store the type.
+        //
+      private:
+        std::uintptr_t data_;
+
+      public:
+        line_type
+        type () const {return static_cast<line_type> (data_ & 0x3);}
+
+        int
+        special () const
+        {
+          // Stored as (shifted) int16_t. Perform steps reversed to those
+          // that are described in the comment for the corresponding ctor.
+          // Note that the intermediate cast to uint16_t is required to
+          // portably preserve the -1 special character.
+          //
+          return static_cast<int16_t> (static_cast<uint16_t> (data_ >> 2));
+        }
+
+        const char_string*
+        literal () const
+        {
+          // Note that 2 rightmost bits are used for packaging line_char
+          // type. Read the comment for the corresponding ctor for details.
+          //
+          return reinterpret_cast<const char_string*> (
+            data_ & ~std::uintptr_t (0x3));
+        }
+
+        const char_regex*
+        regex () const
+        {
+          // Note that 2 rightmost bits are used for packaging line_char
+          // type. Read the comment for the corresponding ctor for details.
+          //
+          return reinterpret_cast<const char_regex*> (
+            data_ & ~std::uintptr_t (0x3));
+        }
+
+        static const line_char nul;
+        static const line_char eof;
+
+        // Note: creates an uninitialized value.
+        //
+        line_char () = default;
+
+        // Create a special character. The argument value must be one of the
+        // following ones:
+        //
+        // 0 (nul character)
+        // -1 (EOF)
+        // [()|.*+?{}\0123456789,=!] (excluding [])
+        //
+        // Note that the constructor is implicit to allow basic_regex to
+        // implicitly construct line_chars from special char literals (in
+        // particular libstdc++ appends them to an internal line_string).
+        //
+        // Also note that we extend the valid characters set (see above) with
+        // 'p', 'n' (used by libstdc++ for positive/negative look-ahead
+        // tokens representation), and '\n', '\r', u'\u2028', u'\u2029' (used
+        // by libstdc++ for newline/newparagraph matching).
+        //
+        line_char (int);
+
+        // Create a literal character.
+        //
+        // Don't copy string if already pooled.
+        //
+        explicit
+        line_char (const char_string&, line_pool&);
+
+        explicit
+        line_char (char_string&&, line_pool&);
+
+        explicit
+        line_char (const char_string* s) // Assume already pooled.
+            //
+            // Steal two bits from the pointer to package line_char type.
+            // Assume (and statically assert) that char_string address is a
+            // multiple of four.
+            //
+            : data_ (reinterpret_cast <std::uintptr_t> (s) |
+                     static_cast <std::uintptr_t> (line_type::literal)) {}
+
+        // Create a regex character.
+        //
+        explicit
+        line_char (char_regex, line_pool&);
+
+        explicit
+        line_char (const char_regex* r) // Assume already pooled.
+            //
+            // Steal two bits from the pointer to package line_char type.
+            // Assume (and statically assert) that char_regex address is a
+            // multiple of four.
+            //
+            : data_ (reinterpret_cast <std::uintptr_t> (r) |
+                     static_cast <std::uintptr_t> (line_type::regex)) {}
+
+        // Provide basic_regex with the ability to use line_char in a context
+        // where a char value is expected (e.g., as a function argument).
+        //
+        // libstdc++ seems to cast special line_chars only (and such a
+        // conversion is meanigfull).
+        //
+        // msvcrt casts line_chars of arbitrary types instead. The only
+        // reasonable strategy is to return a value that differs from any
+        // other that can be encountered in a regex expression and so will
+        // unlikelly be misinterpreted.
+        //
+        operator char () const
+        {
+          return type () == line_type::special ? special () : '\a'; // BELL.
+        }
+
+        // Return true if the character is a syntax (special) one.
+        //
+        static bool
+        syntax (char);
+
+        // Provide basic_regex (such as from msvcrt) with the ability to
+        // explicitly cast line_chars to implementation-specific numeric
+        // types (enums, msvcrt's _Uelem, etc).
+        //
+        template <typename T>
+        explicit
+        operator T () const
+        {
+          assert (type () == line_type::special);
+          return static_cast<T> (special ());
+        }
+      };
+
+      // Perform "deep" characters comparison (for example match literal
+      // character with a regex character), rather than just compare them
+      // literally. At least one argument must be of a type other than regex
+      // as there is no operator==() defined to compare regexes. Characters
+      // of the literal type must share the same pool (strings are compared
+      // by pointers not by values).
+      //
+      bool
+      operator== (const line_char&, const line_char&);
+
+      // Return false if arguments are equal (operator==() returns true).
+      // Otherwise if types are different return the value implying that
+      // special < literal < regex. If types are special or literal return
+      // the result of the respective characters or strings comparison. At
+      // least one argument must be of a type other than regex as there is no
+      // operator<() defined to compare regexes.
+      //
+      // While not very natural operation for the class we have, we have to
+      // provide some meaningfull semantics for such a comparison as it is
+      // required by the char_traits<line_char> specialization. While we
+      // could provide it right in that specialization, let's keep it here
+      // for basic_regex implementations that potentially can compare
+      // line_chars as they compare them with expressions of other types (see
+      // below).
+      //
+      bool
+      operator< (const line_char&, const line_char&);
+
+      inline bool
+      operator!= (const line_char& l, const line_char& r)
+      {
+        return !(l == r);
+      }
+
+      inline bool
+      operator<= (const line_char& l, const line_char& r)
+      {
+        return l < r || l == r;
+      }
+
+      // Provide basic_regex (such as from msvcrt) with the ability to
+      // compare line_char to a value of an integral or
+      // implementation-specific enum type. In the absense of the following
+      // template operators, such a comparisons would be ambigious for
+      // integral types (given that there are implicit conversions
+      // int->line_char and line_char->char) and impossible for enums.
+      //
+      // Note that these == and < operators can succeed only for a line_char
+      // of the special type. For other types they always return false. That
+      // in particular leads to the following case:
+      //
+      // (lc != c) != (lc < c || c < lc).
+      //
+      // Note that we can not assert line_char is of the special type as
+      // basic_regex (such as from libc++) may need the ability to check if
+      // arbitrary line_char belongs to some special characters range (like
+      // ['0', '9']).
+      //
+      template <typename T>
+      struct line_char_cmp
+        : public std::enable_if<std::is_integral<T>::value ||
+      (std::is_enum<T>::value &&
+       !std::is_same<T, char_flags>::value)> {};
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      bool
+      operator== (const line_char& l, const T& r)
+      {
+        return l.type () == line_type::special &&
+          static_cast<T> (l.special ()) == r;
+      }
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      bool
+      operator== (const T& l, const line_char& r)
+      {
+        return r.type () == line_type::special &&
+          static_cast<T> (r.special ()) == l;
+      }
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      bool
+      operator!= (const line_char& l, const T& r)
+      {
+        return !(l == r);
+      }
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      bool
+      operator!= (const T& l, const line_char& r)
+      {
+        return !(l == r);
+      }
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      bool
+      operator< (const line_char& l, const T& r)
+      {
+        return l.type () == line_type::special &&
+          static_cast<T> (l.special ()) < r;
+      }
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      bool
+      operator< (const T& l, const line_char& r)
+      {
+        return r.type () == line_type::special &&
+          l < static_cast<T> (r.special ());
+      }
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      inline bool
+      operator<= (const line_char& l, const T& r)
+      {
+        return l < r || l == r;
+      }
+
+      template <typename T, typename = typename line_char_cmp<T>::type>
+      inline bool
+      operator<= (const T& l, const line_char& r)
+      {
+        return l < r || l == r;
+      }
+
+      using line_string = std::basic_string<line_char>;
+
+      // Locale that has ctype<line_char> facet installed. Used in the
+      // regex_traits<line_char> specialization (see below).
+      //
+      class line_char_locale: public std::locale
+      {
+      public:
+        // Create a copy of the global C++ locale.
+        //
+        line_char_locale ();
+      };
+
+      // Initialize the script regex global state. Should be called once
+      // prior to creating objects of types from this namespace. Note: not
+      // thread-safe.
+      //
+      void
+      init ();
+    }
+  }
+}
+
+// Standard template specializations for line_char that are required for the
+// basic_regex<line_char> instantiation.
+//
+namespace std
+{
+  template <>
+  class char_traits<build2::script::regex::line_char>
+  {
+  public:
+    using char_type  = build2::script::regex::line_char;
+    using int_type   = char_type;
+    using off_type   = char_traits<char>::off_type;
+    using pos_type   = char_traits<char>::pos_type;
+    using state_type = char_traits<char>::state_type;
+
+    static void
+    assign (char_type& c1, const char_type& c2) {c1 = c2;}
+
+    static char_type*
+    assign (char_type*, size_t, char_type);
+
+    // Note that eq() and lt() are not constexpr (as required by C++11)
+    // because == and < operators for char_type are not constexpr.
+    //
+    static bool
+    eq (const char_type& l, const char_type& r) {return l == r;}
+
+    static bool
+    lt (const char_type& l, const char_type& r) {return l < r;}
+
+    static char_type*
+    move (char_type*, const char_type*, size_t);
+
+    static char_type*
+    copy (char_type*, const char_type*, size_t);
+
+    static int
+    compare (const char_type*, const char_type*, size_t);
+
+    static size_t
+    length (const char_type*);
+
+    static const char_type*
+    find (const char_type*, size_t, const char_type&);
+
+    static constexpr char_type
+    to_char_type (const int_type& c) {return c;}
+
+    static constexpr int_type
+    to_int_type (const char_type& c) {return int_type (c);}
+
+    // Note that the following functions are not constexpr (as required by
+    // C++11) because their return expressions are not constexpr.
+    //
+    static bool
+    eq_int_type (const int_type& l, const int_type& r) {return l == r;}
+
+    static int_type eof () {return char_type::eof;}
+
+    static int_type
+    not_eof (const int_type& c)
+    {
+      return c != char_type::eof ? c : char_type::nul;
+    }
+  };
+
+  // ctype<> must be derived from both ctype_base and locale::facet (the later
+  // supports ref-counting used by the std::locale implementation internally).
+  //
+  // msvcrt for some reason also derives ctype_base from locale::facet which
+  // produces "already a base-class" warning and effectivelly breaks the
+  // reference counting. So we derive from ctype_base only in this case.
+  //
+  template <>
+  class ctype<build2::script::regex::line_char>: public ctype_base
+#if !defined(_MSC_VER) || _MSC_VER >= 2000
+                                              , public locale::facet
+#endif
+  {
+    // Used by the implementation only.
+    //
+    using line_type = build2::script::regex::line_type;
+
+  public:
+    using char_type = build2::script::regex::line_char;
+
+    static locale::id id;
+
+#if !defined(_MSC_VER) || _MSC_VER >= 2000
+    explicit
+    ctype (size_t refs = 0): locale::facet (refs) {}
+#else
+    explicit
+    ctype (size_t refs = 0): ctype_base (refs) {}
+#endif
+
+    // While unnecessary, let's keep for completeness.
+    //
+    virtual
+    ~ctype () override = default;
+
+    // The C++ standard requires the following functions to call their virtual
+    // (protected) do_*() counterparts that provide the real implementations.
+    // The only purpose for this indirection is to provide a user with the
+    // ability to customize existing (standard) ctype facets. As we do not
+    // provide such an ability, for simplicity we will omit the do_*()
+    // functions and provide the implementations directly. This should be safe
+    // as nobody except us could call those protected functions.
+    //
+    bool
+    is (mask m, char_type c) const
+    {
+      return m ==
+        (c.type () == line_type::special && c.special () >= 0 &&
+         build2::digit (static_cast<char> (c.special ()))
+         ? digit
+         : 0);
+    }
+
+    const char_type*
+    is (const char_type*, const char_type*, mask*) const;
+
+    const char_type*
+    scan_is (mask, const char_type*, const char_type*) const;
+
+    const char_type*
+    scan_not (mask, const char_type*, const char_type*) const;
+
+    char_type
+    toupper (char_type c) const {return c;}
+
+    const char_type*
+    toupper (char_type*, const char_type* e) const {return e;}
+
+    char_type
+    tolower (char_type c) const {return c;}
+
+    const char_type*
+    tolower (char_type*, const char_type* e) const {return e;}
+
+    char_type
+    widen (char c) const {return char_type (c);}
+
+    const char*
+    widen (const char*, const char*, char_type*) const;
+
+    char
+    narrow (char_type c, char def) const
+    {
+      return c.type () == line_type::special ? c.special () : def;
+    }
+
+    const char_type*
+    narrow (const char_type*, const char_type*, char, char*) const;
+  };
+
+  // Note: the current application locale must be POSIX. Otherwise the
+  // behavior is undefined.
+  //
+  template <>
+  class regex_traits<build2::script::regex::line_char>
+  {
+  public:
+    using char_type       = build2::script::regex::line_char;
+    using string_type     = build2::script::regex::line_string;
+    using locale_type     = build2::script::regex::line_char_locale;
+    using char_class_type = regex_traits<char>::char_class_type;
+
+    // Workaround for msvcrt bugs. For some reason it assumes such a members
+    // to be present in a regex_traits specialization.
+    //
+#if defined(_MSC_VER) && _MSC_VER < 2000
+    static const ctype_base::mask _Ch_upper = ctype_base::upper;
+    static const ctype_base::mask _Ch_alpha = ctype_base::alpha;
+
+    // Unsigned numeric type. msvcrt normally casts characters to this type
+    // for comparing with some numeric values or for calculating an index in
+    // some bit array. Luckily that all relates to the character class
+    // handling that we don't support.
+    //
+    using _Uelem = unsigned int;
+#endif
+
+    regex_traits () = default; // Unnecessary but let's keep for completeness.
+
+    static size_t
+    length (const char_type* p) {return string_type::traits_type::length (p);}
+
+    char_type
+    translate (char_type c) const {return c;}
+
+    // Case-insensitive matching is not supported by line_regex. So there is no
+    // reason for the function to be called.
+    //
+    char_type
+    translate_nocase (char_type c) const {assert (false); return c;}
+
+    // Return a sort-key - the exact copy of [b, e).
+    //
+    template <typename I>
+    string_type
+    transform (I b, I e) const {return string_type (b, e);}
+
+    // Return a case-insensitive sort-key. Case-insensitive matching is not
+    // supported by line_regex. So there is no reason for the function to be
+    // called.
+    //
+    template <typename I>
+    string_type
+    transform_primary (I b, I e) const
+    {
+      assert (false);
+      return string_type (b, e);
+    }
+
+    // POSIX regex grammar and collating elements (e.g., [.tilde.]) in
+    // particular are not supported. So there is no reason for the function to
+    // be called.
+    //
+    template <typename I>
+    string_type
+    lookup_collatename (I, I) const {assert (false); return string_type ();}
+
+    // Character classes (e.g., [:lower:]) are not supported. So there is no
+    // reason for the function to be called.
+    //
+    template <typename I>
+    char_class_type
+    lookup_classname (I, I, bool = false) const
+    {
+      assert (false);
+      return char_class_type ();
+    }
+
+    // Return false as we don't support character classes (e.g., [:lower:]).
+    //
+    bool
+    isctype (char_type, char_class_type) const {return false;}
+
+    int
+    value (char_type, int) const;
+
+    // Return the locale passed as an argument as we do not expect anything
+    // other than POSIX locale, that we also assume to be imbued by default.
+    //
+    locale_type
+    imbue (locale_type l) {return l;}
+
+    locale_type
+    getloc () const {return locale_type ();}
+  };
+
+  // We assume line_char to be an unsigned type and express that with the
+  // following specialization used by basic_regex implementations.
+  //
+  // libstdc++ defines unsigned CharT type (regex_traits template parameter)
+  // to use as an index in some internal cache regardless if the cache is used
+  // for this specialization (and the cache is used only if CharT is char).
+  //
+  template <>
+  struct make_unsigned<build2::script::regex::line_char>
+  {
+    using type = build2::script::regex::line_char;
+  };
+
+  // When used with libc++ the linker complains that it can't find
+  // __match_any_but_newline<line_char>::__exec() function. The problem is
+  // that the function is only specialized for char and wchar_t
+  // (LLVM bug #31409). As line_char has no notion of the newline character we
+  // specialize the class template to behave as the __match_any<line_char>
+  // instantiation does (that luckily has all the functions in place).
+  //
+#if defined(_LIBCPP_VERSION) && _LIBCPP_VERSION <= 9000
+  template <>
+  class __match_any_but_newline<build2::script::regex::line_char>
+    : public __match_any<build2::script::regex::line_char>
+  {
+  public:
+    using base = __match_any<build2::script::regex::line_char>;
+    using base::base;
+  };
+#endif
+}
+
+namespace build2
+{
+  namespace script
+  {
+    namespace regex
+    {
+      class line_regex: public std::basic_regex<line_char>
+      {
+      public:
+        using base_type = std::basic_regex<line_char>;
+
+        using base_type::base_type;
+
+        line_regex () = default;
+
+        // Move string regex together with the pool used to create it.
+        //
+        line_regex (line_string&& s, line_pool&& p)
+            // No move-string ctor for base_type, so emulate it.
+            //
+            : base_type (s), pool (move (p)) {s.clear ();}
+
+        // Move constuctible/assignable-only type.
+        //
+        line_regex (line_regex&&) = default;
+        line_regex (const line_regex&) = delete;
+        line_regex& operator= (line_regex&&) = default;
+        line_regex& operator= (const line_regex&) = delete;
+
+      public:
+        line_pool pool;
+      };
+    }
+  }
+}
+
+#include <libbuild2/script/regex.ixx>
+
+#endif // LIBBUILD2_SCRIPT_REGEX_HXX
diff --git a/libbuild2/script/regex.ixx b/libbuild2/script/regex.ixx
new file mode 100644
index 0000000..e72b578
--- /dev/null
+++ b/libbuild2/script/regex.ixx
@@ -0,0 +1,31 @@
+// file      : libbuild2/script/regex.ixx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+namespace build2
+{
+  namespace script
+  {
+    namespace regex
+    {
+      inline char_flags
+      operator&= (char_flags& x, char_flags y)
+      {
+        return x = static_cast<char_flags> (
+          static_cast<uint16_t> (x) & static_cast<uint16_t> (y));
+      }
+
+      inline char_flags
+      operator|= (char_flags& x, char_flags y)
+      {
+        return x = static_cast<char_flags> (
+          static_cast<uint16_t> (x) | static_cast<uint16_t> (y));
+      }
+
+      inline char_flags
+      operator& (char_flags x, char_flags y) {return x &= y;}
+
+      inline char_flags
+      operator| (char_flags x, char_flags y) {return x |= y;}
+    }
+  }
+}
diff --git a/libbuild2/script/regex.test.cxx b/libbuild2/script/regex.test.cxx
new file mode 100644
index 0000000..36d47e1
--- /dev/null
+++ b/libbuild2/script/regex.test.cxx
@@ -0,0 +1,303 @@
+// file      : libbuild2/script/regex.test.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <regex>
+#include <type_traits> // is_*
+
+#include <libbuild2/script/regex.hxx>
+
+using namespace std;
+using namespace build2::script::regex;
+
+int
+main ()
+{
+  using lc = line_char;
+  using ls = line_string;
+  using lr = line_regex;
+  using cf = char_flags;
+  using cr = char_regex;
+
+  init (); // Initializes the script regex global state.
+
+  // Test line_char.
+  //
+  {
+    static_assert (is_trivial<lc>::value         &&
+                   is_standard_layout<lc>::value &&
+                   !is_array<lc>::value,
+                   "line_char must be char-like");
+
+    // Zero-initialed line_char should be the null-char as required by
+    // char_traits<>::length() specification.
+    //
+    assert (lc () == lc::nul);
+
+    line_pool p;
+
+    assert (lc::eof == -1);
+    assert (lc::nul == 0);
+
+    enum meta {mn = 'n', mp = 'p'};
+
+    // Special roundtrip.
+    //
+    assert (lc ('0').special ()       == '0');
+    assert (lc (0).special ()         == 0);
+    assert (lc (-1).special ()        == -1);
+    assert (lc ('p').special ()       == 'p');
+    assert (lc (u'\u2028').special () == u'\u2028');
+
+    // Special comparison.
+    //
+    assert (lc ('0') == lc ('0'));
+    assert (lc ('0') == '0');
+    assert (lc ('n') == mn);
+    assert (mn       == static_cast<meta> (lc ('n')));
+
+    assert (lc ('0') != lc ('1'));
+    assert (lc ('0') != '1');
+    assert (lc ('n') != mp);
+    assert (lc ('0') != lc ("0", p));
+    assert (lc ('0') != lc (cr ("0"), p));
+
+    assert (lc ('0') < lc ('1'));
+    assert (lc ('0') < '1');
+    assert (lc ('1') < lc ("0", p));
+    assert (lc ('n') < mp);
+
+    assert (lc ('0') <= '1');
+    assert (lc ('0') <= lc ('1'));
+    assert (lc ('n') <= mn);
+    assert (lc ('1') <= lc ("0", p));
+
+    // Literal roundtrip.
+    //
+    assert (*lc ("abc", p).literal () == "abc");
+
+    // Literal comparison.
+    //
+    assert (lc ("a", p)            == lc ("a", p));
+    assert (lc ("a", p).literal () == lc ("a", p).literal ());
+    assert (char (lc ("a", p))     == '\a');
+
+    assert (lc ("a", p)   != lc ("b", p));
+    assert (!(lc ("a", p) != lc (cr ("a"), p)));
+    assert (lc ("a", p)   != lc (cr ("b"), p));
+
+    assert (lc ("a", p)   < lc ("b", p));
+    assert (!(lc ("a", p) < lc (cr ("a"), p)));
+
+    assert (lc ("a", p) <= lc ("b", p));
+    assert (lc ("a", p) <= lc (cr ("a"), p));
+    assert (lc ("a", p) <  lc (cr ("c"), p));
+
+    // Regex roundtrip.
+    //
+    assert (regex_match ("abc", *lc (cr ("abc"), p).regex ()));
+
+    // Regex flags.
+    //
+    // icase
+    //
+    assert (regex_match ("ABC", cr ("abc", cf::icase)));
+
+    // idot
+    //
+    assert (!regex_match ("a", cr ("[.]",  cf::idot)));
+    assert (!regex_match ("a", cr ("[\\.]", cf::idot)));
+
+    assert (regex_match  ("a", cr (".")));
+    assert (!regex_match ("a", cr (".", cf::idot)));
+    assert (regex_match  ("a", cr ("\\.", cf::idot)));
+    assert (!regex_match ("a", cr ("\\.")));
+
+    // regex::transform()
+    //
+    // The function is static and we can't test it directly. So we will test
+    // it indirectly via regex matches.
+    //
+    // @@ Would be nice to somehow address the inability to test internals (not
+    //    exposed via headers). As a part of utility library support?
+    //
+    assert (regex_match  (".a[.", cr (".\\.\\[[.]",   cf::idot)));
+    assert (regex_match  (".a[.", cr (".\\.\\[[\\.]", cf::idot)));
+    assert (!regex_match ("ba[.", cr (".\\.\\[[.]",   cf::idot)));
+    assert (!regex_match (".a[b", cr (".\\.\\[[.]",   cf::idot)));
+    assert (!regex_match (".a[b", cr (".\\.\\[[\\.]", cf::idot)));
+
+    // Regex comparison.
+    //
+    assert (lc ("a", p)        == lc (cr ("a|b"), p));
+    assert (lc (cr ("a|b"), p) == lc ("a", p));
+  }
+
+  // Test char_traits<line_char>.
+  //
+  {
+    using ct = char_traits<lc>;
+    using vc = vector<lc>;
+
+    lc c;
+    ct::assign (c, '0');
+    assert (c == ct::char_type ('0'));
+
+    assert (ct::to_char_type (c) == c);
+    assert (ct::to_int_type (c) == c);
+
+    assert (ct::eq_int_type (c, c));
+    assert (!ct::eq_int_type (c, lc::eof));
+
+    assert (ct::eof () == lc::eof);
+
+    assert (ct::not_eof (c) == c);
+    assert (ct::not_eof (lc::eof) != lc::eof);
+
+    ct::assign (&c, 1, '1');
+    assert (c == ct::int_type ('1'));
+
+    assert (ct::eq (lc ('0'), lc ('0')));
+    assert (ct::lt (lc ('0'), lc ('1')));
+
+    vc v1 ({'0', '1', '2'});
+    vc v2 (3, lc::nul);
+
+    assert (ct::find (v1.data (), 3, '1') == v1.data () + 1);
+
+    ct::copy (v2.data (), v1.data (), 3);
+    assert (v2 == v1);
+
+    v2.push_back (lc::nul);
+    assert (ct::length (v2.data ()) == 3);
+
+    // Overlaping ranges.
+    //
+    ct::move (v1.data () + 1, v1.data (), 2);
+    assert (v1 == vc ({'0', '0', '1'}));
+
+    v1 = vc ({'0', '1', '2'});
+    ct::move (v1.data (), v1.data () + 1, 2);
+    assert (v1 == vc ({'1', '2', '2'}));
+  }
+
+  // Test line_char_locale and ctype<line_char> (only non-trivial functions).
+  //
+  {
+    using ct = ctype<lc>;
+
+    line_char_locale l;
+
+    // It is better not to create q facet on stack as it is
+    // reference-countable.
+    //
+    const ct& t (use_facet<ct> (l));
+    line_pool p;
+
+    assert (t.is  (ct::digit, '0'));
+    assert (!t.is (ct::digit, '?'));
+    assert (!t.is (ct::digit, lc ("0", p)));
+
+    const lc chars[] = { '0', '?' };
+    ct::mask m[2];
+
+    const lc* b (chars);
+    const lc* e (chars + 2);
+
+    // Cast flag value to mask type and compare to mask.
+    //
+    auto fl = [] (ct::mask m, ct::mask f) {return m == f;};
+
+    t.is (b, e, m);
+    assert (fl (m[0], ct::digit) && fl (m[1], 0));
+
+    assert (t.scan_is (ct::digit, b, e) == b);
+    assert (t.scan_is (0, b, e) == b + 1);
+
+    assert (t.scan_not (ct::digit, b, e) == b + 1);
+    assert (t.scan_not (0, b, e) == b);
+
+    {
+      char nr[] = "0?";
+      lc wd[2];
+      t.widen (nr, nr + 2, wd);
+      assert (wd[0] == b[0] && wd[1] == b[1]);
+    }
+
+    {
+      lc wd[] = {'0', lc ("a", p)};
+      char nr[2];
+      t.narrow (wd, wd + 2, '-', nr);
+      assert (nr[0] == '0' && nr[1] == '-');
+    }
+  }
+
+  // Test regex_traits<line_char>. Functions other that value() are trivial.
+  //
+  {
+    regex_traits<lc> t;
+
+    const int  radix[] = {8, 10}; // Radix 16 is not supported by line_char.
+    const char digits[] = "0123456789ABCDEF";
+
+    for (size_t r (0); r < 2; ++r)
+    {
+      for (int i (0); i < radix[r]; ++i)
+        assert (t.value (digits[i], radix[r]) == i);
+    }
+  }
+
+  // Test line_regex construction.
+  //
+  {
+    line_pool p;
+    lr r1 ({lc ("foo", p), lc (cr ("ba(r|z)"), p)}, move (p));
+
+    lr r2 (move (r1));
+    assert (regex_match (ls ({lc ("foo", r2.pool), lc ("bar", r2.pool)}), r2));
+    assert (!regex_match (ls ({lc ("foo", r2.pool), lc ("ba", r2.pool)}), r2));
+  }
+
+  // Test line_regex match.
+  //
+  {
+    line_pool p;
+
+    const lc foo ("foo", p);
+    const lc bar ("bar", p);
+    const lc baz ("baz", p);
+    const lc blank ("", p);
+
+    assert (regex_match  (ls ({foo, bar}), lr ({foo, bar})));
+    assert (!regex_match (ls ({foo, baz}), lr ({foo, bar})));
+
+    assert (regex_match (ls ({bar, foo}),
+                         lr ({'(', foo, '|', bar, ')', '+'})));
+
+    assert (regex_match (ls ({foo, foo, bar}),
+                         lr ({'(', foo, ')', '\\', '1', bar})));
+
+    assert (regex_match (ls ({foo}),   lr ({lc (cr ("fo+"), p)})));
+    assert (regex_match (ls ({foo}),   lr ({lc (cr (".*"), p)})));
+    assert (regex_match (ls ({blank}), lr ({lc (cr (".*"), p)})));
+
+    assert (regex_match (ls ({blank, blank, foo}),
+                         lr ({blank, '*', foo, blank, '*'})));
+
+    assert (regex_match (ls ({blank, blank, foo}), lr ({'.', '*'})));
+
+    assert (regex_match (ls ({blank, blank}),
+                         lr ({blank, '*', foo, '?', blank, '*'})));
+
+    assert (regex_match  (ls ({foo}),      lr ({foo, '{', '1', '}'})));
+    assert (regex_match  (ls ({foo, foo}), lr ({foo, '{', '1', ',', '}'})));
+
+    assert (regex_match  (ls ({foo, foo}),
+                          lr ({foo, '{', '1', ',', '2', '}'})));
+
+    assert (!regex_match (ls ({foo, foo}),
+                          lr ({foo, '{', '3', ',', '4', '}'})));
+
+    assert (regex_match  (ls ({foo}), lr ({'(', '?', '=', foo, ')', foo})));
+    assert (regex_match  (ls ({foo}), lr ({'(', '?', '!', bar, ')', foo})));
+  }
+}
diff --git a/libbuild2/script/run.cxx b/libbuild2/script/run.cxx
new file mode 100644
index 0000000..38436b9
--- /dev/null
+++ b/libbuild2/script/run.cxx
@@ -0,0 +1,2020 @@
+// file      : libbuild2/script/run.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/script/run.hxx>
+
+#include <ios> // streamsize
+
+#include <libbutl/regex.mxx>
+#include <libbutl/builtin.mxx>
+#include <libbutl/fdstream.mxx>     // fdopen_mode, fddup()
+#include <libbutl/filesystem.mxx>   // path_search()
+#include <libbutl/path-pattern.mxx>
+
+#include <libbuild2/filesystem.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/script/regex.hxx>
+#include <libbuild2/script/builtin-options.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  namespace script
+  {
+    string
+    diag_path (const path& d)
+    {
+      string r ("'");
+
+      r += stream_verb_map ().path < 1
+           ? diag_relative (d)
+           : d.representation ();
+
+      r += '\'';
+      return r;
+    }
+
+    string
+    diag_path (const dir_name_view& dn)
+    {
+      string r;
+      if (dn.name != nullptr && *dn.name)
+      {
+        r += **dn.name;
+        r += ' ';
+      }
+
+      assert (dn.path != nullptr);
+
+      r += diag_path (*dn.path);
+      return r;
+    }
+
+    // Return the environment temporary directory, creating it if it doesn't
+    // exist.
+    //
+    static inline const dir_path&
+    temp_dir (environment& env)
+    {
+      if (env.temp_dir.empty ())
+        env.create_temp_dir ();
+
+      return env.temp_dir;
+    }
+
+    // Normalize a path. Also make the relative path absolute using the
+    // specified directory unless it is already absolute.
+    //
+    static path
+    normalize (path p, const dir_path& d, const location& l)
+    {
+      path r (p.absolute () ? move (p) : d / move (p));
+
+      try
+      {
+        r.normalize ();
+      }
+      catch (const invalid_path& e)
+      {
+        fail (l) << "invalid file path " << e.path;
+      }
+
+      return r;
+    }
+
+    // Check if a path is not empty, the referenced file exists and is not
+    // empty.
+    //
+    static bool
+    non_empty (const path& p, const location& ll)
+    {
+      if (p.empty () || !exists (p))
+        return false;
+
+      try
+      {
+        ifdstream is (p);
+        return is.peek () != ifdstream::traits_type::eof ();
+      }
+      catch (const io_error& e)
+      {
+        // While there can be no fault of the script command being currently
+        // executed let's add the location anyway to ease the
+        // troubleshooting. And let's stick to that principle down the road.
+        //
+        fail (ll) << "unable to read " << p << ": " << e << endf;
+      }
+    }
+
+    // If the file exists, not empty and not larger than 4KB print it to the
+    // diag record. The file content goes from the new line and is not
+    // indented.
+    //
+    static void
+    print_file (diag_record& d, const path& p, const location& ll)
+    {
+      if (exists (p))
+      {
+        try
+        {
+          ifdstream is (p, ifdstream::badbit);
+
+          if (is.peek () != ifdstream::traits_type::eof ())
+          {
+            char buf[4096 + 1]; // Extra byte is for terminating '\0'.
+
+            // Note that the string is always '\0'-terminated with a maximum
+            // sizeof (buf) - 1 bytes read.
+            //
+            is.getline (buf, sizeof (buf), '\0');
+
+            // Print if the file fits 4KB-size buffer. Note that if it
+            // doesn't the failbit is set.
+            //
+            if (is.eof ())
+            {
+              // Suppress the trailing newline character as the diag record
+              // adds it's own one when flush.
+              //
+              streamsize n (is.gcount ());
+              assert (n > 0);
+
+              // Note that if the file contains '\0' it will also be counted
+              // by gcount(). But even in the worst case we will stay in the
+              // buffer boundaries (and so not crash).
+              //
+              if (buf[n - 1] == '\n')
+                buf[n - 1] = '\0';
+
+              d << '\n' << buf;
+            }
+          }
+        }
+        catch (const io_error& e)
+        {
+          fail (ll) << "unable to read " << p << ": " << e;
+        }
+      }
+    }
+
+    // Save a string to the file. Fail if exception is thrown by underlying
+    // operations.
+    //
+    static void
+    save (const path& p, const string& s, const location& ll)
+    {
+      try
+      {
+        ofdstream os (p);
+        os << s;
+        os.close ();
+      }
+      catch (const io_error& e)
+      {
+        fail (ll) << "unable to write to " << p << ": " << e;
+      }
+    }
+
+    // Transform string according to here-* redirect modifiers from the {/}
+    // set.
+    //
+    static string
+    transform (const string& s,
+               bool regex,
+               const string& modifiers,
+               environment& env)
+    {
+      if (modifiers.find ('/') == string::npos)
+        return s;
+
+      // For targets other than Windows leave the string intact.
+      //
+      if (env.host.class_ != "windows")
+        return s;
+
+      // Convert forward slashes to Windows path separators (escape for
+      // regex).
+      //
+      string r;
+      for (size_t p (0);;)
+      {
+        size_t sp (s.find ('/', p));
+
+        if (sp != string::npos)
+        {
+          r.append (s, p, sp - p);
+          r.append (regex ? "\\\\" : "\\");
+          p = sp + 1;
+        }
+        else
+        {
+          r.append (s, p, sp);
+          break;
+        }
+      }
+
+      return r;
+    }
+
+    // Return true if the script temporary directory is not created yet (and
+    // so cannot contain any path), a path is not under the temporary
+    // directory or this directory will not be removed on failure.
+    //
+    static inline bool
+    avail_on_failure (const path& p, const environment& env)
+    {
+      return env.temp_dir.empty () ||
+             env.temp_dir_keep     ||
+             !p.sub (env.temp_dir);
+    }
+
+    // Check if the script command output matches the expected result
+    // (redirect value). Noop for redirect types other than none, here_*.
+    //
+    static bool
+    check_output (const path& pr,
+                  const path& op,
+                  const path& ip,
+                  const redirect& rd,
+                  const location& ll,
+                  environment& env,
+                  bool diag,
+                  const char* what)
+    {
+      auto input_info = [&ip, &ll, &env] (diag_record& d)
+      {
+        if (non_empty (ip, ll) && avail_on_failure (ip, env))
+          d << info << "stdin: " << ip;
+      };
+
+      auto output_info = [&what, &ll, &env] (diag_record& d,
+                                             const path& p,
+                                             const char* prefix = "",
+                                             const char* suffix = "")
+      {
+        if (non_empty (p, ll))
+        {
+          if (avail_on_failure (p, env))
+            d << info << prefix << what << suffix << ": " << p;
+        }
+        else
+          d << info << prefix << what << suffix << " is empty";
+      };
+
+      if (rd.type == redirect_type::none)
+      {
+        // Check that there is no output produced.
+        //
+        assert (!op.empty ());
+
+        if (!non_empty (op, ll))
+          return true;
+
+        if (diag)
+        {
+          diag_record d (error (ll));
+          d << pr << " unexpectedly writes to " << what;
+
+          if (avail_on_failure (op, env))
+            d << info << what << ": " << op;
+
+          input_info (d);
+
+          // Print cached output.
+          //
+          print_file (d, op, ll);
+        }
+
+        // Fall through (to return false).
+        //
+      }
+      else if (rd.type == redirect_type::here_str_literal ||
+               rd.type == redirect_type::here_doc_literal ||
+               (rd.type == redirect_type::file &&
+                rd.file.mode == redirect_fmode::compare))
+      {
+        // The expected output is provided as a file or as a string. Save the
+        // string to a file in the later case.
+        //
+        assert (!op.empty ());
+
+        path eop;
+
+        if (rd.type == redirect_type::file)
+          eop = normalize (rd.file.path, *env.work_dir.path, ll);
+        else
+        {
+          eop = path (op + ".orig");
+
+          save (eop,
+                transform (rd.str, false /* regex */, rd.modifiers (), env),
+                ll);
+
+          env.clean_special (eop);
+        }
+
+        // Use the diff utility for comparison.
+        //
+        path dp ("diff");
+        process_path pp (run_search (dp, true));
+
+        cstrings args {pp.recall_string ()};
+
+        // If both files being compared won't be available on failure, then
+        // instruct diff not to print the file paths. It seems that the only
+        // way to achieve this is to abandon the output unified format in the
+        // favor of the minimal output, which normally is still informative
+        // enough for the troubleshooting (contains the difference line
+        // numbers, etc).
+        //
+        if (avail_on_failure (eop, env) || avail_on_failure (op, env))
+          args.push_back ("-u");
+
+        // Ignore Windows newline fluff if that's what we are running on.
+        //
+        if (env.host.class_ == "windows")
+          args.push_back ("--strip-trailing-cr");
+
+        args.push_back (eop.string ().c_str ());
+        args.push_back (op.string ().c_str ());
+        args.push_back (nullptr);
+
+        if (verb >= 2)
+          print_process (args);
+
+        try
+        {
+          // Save diff's stdout to a file for troubleshooting and for the
+          // optional (if not too large) printing (at the end of
+          // diagnostics).
+          //
+          path ep (op + ".diff");
+          auto_fd efd;
+
+          try
+          {
+            efd = fdopen (ep, fdopen_mode::out | fdopen_mode::create);
+            env.clean_special (ep);
+          }
+          catch (const io_error& e)
+          {
+            fail (ll) << "unable to write to " << ep << ": " << e;
+          }
+
+          // Diff utility prints the differences to stdout. But for the
+          // user it is a part of the script failure diagnostics so let's
+          // redirect stdout to stderr.
+          //
+          process p (pp, args.data (), 0, 2, efd.get ());
+          efd.reset ();
+
+          if (p.wait ())
+            return true;
+
+          assert (p.exit);
+          const process_exit& pe (*p.exit);
+
+          // Note that both POSIX and GNU diff report error by exiting with
+          // the code > 1.
+          //
+          if (!pe.normal () || pe.code () > 1)
+          {
+            diag_record d (fail (ll));
+            print_process (d, args);
+            d << " " << pe;
+
+            print_file (d, ep, ll);
+          }
+
+          // Output doesn't match the expected result.
+          //
+          if (diag)
+          {
+            diag_record d (error (ll));
+            d << pr << " " << what << " doesn't match expected";
+
+            output_info (d, op);
+            output_info (d, eop, "expected ");
+            output_info (d, ep, "", " diff");
+            input_info  (d);
+
+            print_file (d, ep, ll);
+          }
+
+          // Fall through (to return false).
+          //
+        }
+        catch (const process_error& e)
+        {
+          error (ll) << "unable to execute " << pp << ": " << e;
+
+          if (e.child)
+            exit (1);
+
+          throw failed ();
+        }
+      }
+      else if (rd.type == redirect_type::here_str_regex ||
+               rd.type == redirect_type::here_doc_regex)
+      {
+        // The overall plan is:
+        //
+        // 1. Create regex line string. While creating it's line characters
+        //    transform regex lines according to the redirect modifiers.
+        //
+        // 2. Create line regex using the line string. If creation fails
+        //    then save the (transformed) regex redirect to a file for
+        //    troubleshooting.
+        //
+        // 3. Parse the output into the literal line string.
+        //
+        // 4. Match the output line string with the line regex.
+        //
+        // 5. If match fails save the (transformed) regex redirect to a file
+        //    for troubleshooting.
+        //
+        using namespace regex;
+
+        assert (!op.empty ());
+
+        // Create regex line string.
+        //
+        line_pool pool;
+        line_string rls;
+        const regex_lines rl (rd.regex);
+
+        // Parse regex flags.
+        //
+        // When add support for new flags don't forget to update
+        // parse_regex().
+        //
+        auto parse_flags = [] (const string& f) -> char_flags
+        {
+          char_flags r (char_flags::none);
+
+          for (char c: f)
+          {
+            switch (c)
+            {
+            case 'd': r |= char_flags::idot;  break;
+            case 'i': r |= char_flags::icase; break;
+            default: assert (false); // Error so should have been checked.
+            }
+          }
+
+          return r;
+        };
+
+        // Return original regex line with the transformation applied.
+        //
+        auto line = [&rl, &rd, &env] (const regex_line& l) -> string
+        {
+          string r;
+          if (l.regex)                  // Regex (possibly empty),
+          {
+            r += rl.intro;
+            r += transform (l.value, true /* regex */, rd.modifiers (), env);
+            r += rl.intro;
+            r += l.flags;
+          }
+          else if (!l.special.empty ()) // Special literal.
+            r += rl.intro;
+          else                          // Textual literal.
+            r += transform (l.value, false /* regex */, rd.modifiers (), env);
+
+          r += l.special;
+          return r;
+        };
+
+        // Return regex line location.
+        //
+        // Note that we rely on the fact that the command and regex lines
+        // are always belong to the same file.
+        //
+        auto loc = [&ll] (uint64_t line, uint64_t column) -> location
+        {
+          location r (ll);
+          r.line = line;
+          r.column = column;
+          return r;
+        };
+
+        // Save the regex to file for troubleshooting, return the file path
+        // it have been saved to.
+        //
+        // Note that we save the regex on line regex creation failure or if
+        // the program output doesn't match.
+        //
+        auto save_regex = [&op, &rl, &rd, &ll, &line] () -> path
+        {
+          path rp (op + ".regex");
+
+          // Encode here-document regex global flags if present as a file
+          // name suffix. For example if icase and idot flags are specified
+          // the name will look like:
+          //
+          // stdout.regex-di
+          //
+          if (rd.type == redirect_type::here_doc_regex && !rl.flags.empty ())
+            rp += '-' + rl.flags;
+
+          // Note that if would be more efficient to directly write chunks
+          // to file rather than to compose a string first. Hower we don't
+          // bother (about performance) for the sake of the code as we
+          // already failed.
+          //
+          string s;
+          for (auto b (rl.lines.cbegin ()), i (b), e (rl.lines.cend ());
+               i != e; ++i)
+          {
+            if (i != b) s += '\n';
+            s += line (*i);
+          }
+
+          save (rp, s, ll);
+          return rp;
+        };
+
+        // Finally create regex line string.
+        //
+        // Note that diagnostics doesn't refer to the program path as it is
+        // irrelevant to failures at this stage.
+        //
+        char_flags gf (parse_flags (rl.flags)); // Regex global flags.
+
+        for (const auto& l: rl.lines)
+        {
+          if (l.regex) // Regex (with optional special characters).
+          {
+            line_char c;
+
+            // Empty regex is a special case repesenting the blank line.
+            //
+            if (l.value.empty ())
+              c = line_char ("", pool);
+            else
+            {
+              try
+              {
+                string s (transform (l.value,
+                                     true /* regex */,
+                                     rd.modifiers (),
+                                     env));
+
+                c = line_char (
+                  char_regex (s, gf | parse_flags (l.flags)), pool);
+              }
+              catch (const regex_error& e)
+              {
+                // Print regex_error description if meaningful.
+                //
+                diag_record d (fail (loc (l.line, l.column)));
+
+                if (rd.type == redirect_type::here_str_regex)
+                  d << "invalid " << what << " regex redirect" << e <<
+                    info << "regex: '" << line (l) << "'";
+                else
+                  d << "invalid char-regex in " << what << " regex redirect"
+                    << e <<
+                    info << "regex line: '" << line (l) << "'";
+
+                d << endf;
+              }
+            }
+
+            rls += c; // Append blank literal or regex line char.
+          }
+          else if (!l.special.empty ()) // Special literal.
+          {
+            // Literal can not be followed by special characters in the same
+            // line.
+            //
+            assert (l.value.empty ());
+          }
+          else // Textual literal.
+          {
+            // Append literal line char.
+            //
+            rls += line_char (transform (l.value,
+                                         false /* regex */,
+                                         rd.modifiers (),
+                                         env),
+                              pool);
+          }
+
+          for (char c: l.special)
+          {
+            if (line_char::syntax (c))
+              rls += line_char (c); // Append special line char.
+            else
+              fail (loc (l.line, l.column))
+                << "invalid syntax character '" << c << "' in " << what
+                << " regex redirect" <<
+                info << "regex line: '" << line (l) << "'";
+          }
+        }
+
+        // Create line regex.
+        //
+        line_regex regex;
+
+        try
+        {
+          regex = line_regex (move (rls), move (pool));
+        }
+        catch (const regex_error& e)
+        {
+          // Note that line regex creation can not fail for here-string
+          // redirect as it doesn't have syntax line chars. That in
+          // particular means that end_line and end_column are meaningful.
+          //
+          assert (rd.type == redirect_type::here_doc_regex);
+
+          diag_record d (fail (loc (rd.end_line, rd.end_column)));
+
+          // Print regex_error description if meaningful.
+          //
+          d << "invalid " << what << " regex redirect" << e;
+
+          // It would be a waste to save the regex into the file just to
+          // remove it.
+          //
+          if (env.temp_dir_keep)
+            output_info (d, save_regex (), "", " regex");
+        }
+
+        // Parse the output into the literal line string.
+        //
+        line_string ls;
+
+        try
+        {
+          // Do not throw when eofbit is set (end of stream reached), and
+          // when failbit is set (getline() failed to extract any character).
+          //
+          // Note that newlines are treated as line-chars separators. That
+          // in particular means that the trailing newline produces a blank
+          // line-char (empty literal). Empty output produces the zero-length
+          // line-string.
+          //
+          // Also note that we strip the trailing CR characters (otherwise
+          // can mismatch when, for example, cross-testing).
+          //
+          ifdstream is (op, ifdstream::badbit);
+          is.peek (); // Sets eofbit for an empty stream.
+
+          while (!is.eof ())
+          {
+            string s;
+            getline (is, s);
+
+            // It is safer to strip CRs in cycle, as msvcrt unexplainably
+            // adds too much trailing junk to the system_error descriptions,
+            // and so it can appear in programs output. For example:
+            //
+            // ...: Invalid data.\r\r\n
+            //
+            // Note that our custom operator<<(ostream&, const exception&)
+            // removes this junk.
+            //
+            while (!s.empty () && s.back () == '\r')
+              s.pop_back ();
+
+            ls += line_char (move (s), regex.pool);
+          }
+        }
+        catch (const io_error& e)
+        {
+          fail (ll) << "unable to read " << op << ": " << e;
+        }
+
+        // Match the output with the regex.
+        //
+        if (regex_match (ls, regex)) // Doesn't throw.
+          return true;
+
+        // Output doesn't match the regex.
+        //
+        // Unless the temporary directory is removed on failure, we save the
+        // regex to file for troubleshooting regardless of whether we print
+        // the diagnostics or not. We, however, register it for cleanup in the
+        // later case (the expression may still succeed, we can be evaluating
+        // the if condition, etc).
+        //
+        optional<path> rp;
+        if (env.temp_dir_keep)
+          rp = save_regex ();
+
+        if (diag)
+        {
+          diag_record d (error (ll));
+          d << pr << " " << what << " doesn't match regex";
+
+          output_info (d, op);
+
+          if (rp)
+            output_info (d, *rp, "", " regex");
+
+          input_info  (d);
+
+          // Print cached output.
+          //
+          print_file (d, op, ll);
+        }
+        else if (rp)
+          env.clean_special (*rp);
+
+        // Fall through (to return false).
+        //
+      }
+      else // Noop.
+        return true;
+
+      return false;
+    }
+
+    // The exit pseudo-builtin: exit the script successfully, or print the
+    // diagnostics and exit the script unsuccessfully. Always throw exit
+    // exception.
+    //
+    // exit [<diagnostics>]
+    //
+    [[noreturn]] static void
+    exit_builtin (const strings& args, const location& ll)
+    {
+      auto i (args.begin ());
+      auto e (args.end ());
+
+      // Process arguments.
+      //
+      // If no argument is specified, then exit successfully. Otherwise,
+      // print the diagnostics and exit unsuccessfully.
+      //
+      if (i == e)
+        throw exit (true);
+
+      const string& s (*i++);
+
+      if (i != e)
+        fail (ll) << "unexpected argument '" << *i << "'";
+
+      error (ll) << s;
+      throw exit (false);
+    }
+
+    // The set pseudo-builtin: set variable from the stdin input.
+    //
+    // set [-e|--exact] [(-n|--newline)|(-w|--whitespace)] [<attr>] <var>
+    //
+    static void
+    set_builtin (environment& env,
+                 const strings& args,
+                 auto_fd in,
+                 const location& ll)
+    {
+      try
+      {
+        // Do not throw when eofbit is set (end of stream reached), and
+        // when failbit is set (read operation failed to extract any
+        // character).
+        //
+        ifdstream cin  (move (in), ifdstream::badbit);
+
+        // Parse arguments.
+        //
+        cli::vector_scanner scan (args);
+        set_options ops (scan);
+
+        if (ops.whitespace () && ops.newline ())
+          fail (ll) << "both -n|--newline and -w|--whitespace specified";
+
+        if (!scan.more ())
+          fail (ll) << "missing variable name";
+
+        string a (scan.next ()); // Either attributes or variable name.
+        const string* ats (!scan.more () ? nullptr : &a);
+        string vname (!scan.more () ? move (a) : scan.next ());
+
+        if (scan.more ())
+          fail (ll) << "unexpected argument '" << scan.next () << "'";
+
+        if (ats != nullptr && ats->empty ())
+          fail (ll) << "empty variable attributes";
+
+        if (vname.empty ())
+          fail (ll) << "empty variable name";
+
+        // Read the input.
+        //
+        cin.peek (); // Sets eofbit for an empty stream.
+
+        names ns;
+        while (!cin.eof ())
+        {
+          // Read next element that depends on the whitespace mode being
+          // enabled or not. For the later case it also make sense to strip
+          // the trailing CRs that can appear while, for example,
+          // cross-testing Windows target or as a part of msvcrt junk
+          // production (see above).
+          //
+          string s;
+          if (ops.whitespace ())
+            cin >> s;
+          else
+          {
+            getline (cin, s);
+
+            while (!s.empty () && s.back () == '\r')
+              s.pop_back ();
+          }
+
+          // If failbit is set then we read nothing into the string as eof is
+          // reached. That in particular means that the stream has trailing
+          // whitespaces (possibly including newlines) if the whitespace mode
+          // is enabled, or the trailing newline otherwise. If so then
+          // we append the "blank" to the variable value in the exact mode
+          // prior to bailing out.
+          //
+          if (cin.fail ())
+          {
+            if (ops.exact ())
+            {
+              if (ops.whitespace () || ops.newline ())
+                ns.emplace_back (move (s)); // Reuse empty string.
+              else if (ns.empty ())
+                ns.emplace_back ("\n");
+              else
+                ns[0].value += '\n';
+            }
+
+            break;
+          }
+
+          if (ops.whitespace () || ops.newline () || ns.empty ())
+            ns.emplace_back (move (s));
+          else
+          {
+            ns[0].value += '\n';
+            ns[0].value += s;
+          }
+        }
+
+        cin.close ();
+
+        env.set_variable (move (vname),
+                          move (ns),
+                          ats != nullptr ? *ats : empty_string,
+                          ll);
+      }
+      catch (const io_error& e)
+      {
+        fail (ll) << "set: " << e;
+      }
+      catch (const cli::exception& e)
+      {
+        fail (ll) << "set: " << e;
+      }
+    }
+
+    // Sorted array of builtins that support filesystem entries cleanup.
+    //
+    static const char* cleanup_builtins[] = {
+      "cp", "ln", "mkdir", "mv", "touch"};
+
+    static inline bool
+    cleanup_builtin (const string& name)
+    {
+      return binary_search (
+        cleanup_builtins,
+        cleanup_builtins +
+        sizeof (cleanup_builtins) / sizeof (*cleanup_builtins),
+        name);
+    }
+
+    static bool
+    run_pipe (environment& env,
+              command_pipe::const_iterator bc,
+              command_pipe::const_iterator ec,
+              auto_fd ifd,
+              size_t ci, size_t li, const location& ll,
+              bool diag)
+    {
+      if (bc == ec) // End of the pipeline.
+        return true;
+
+      // The overall plan is to run the first command in the pipe, reading
+      // its input from the file descriptor passed (or, for the first
+      // command, according to stdin redirect specification) and redirecting
+      // its output to the right-hand part of the pipe recursively. Fail if
+      // the right-hand part fails. Otherwise check the process exit code,
+      // match stderr (and stdout for the last command in the pipe) according
+      // to redirect specification(s) and fail if any of the above fails.
+      //
+      const command& c (*bc);
+
+      // Register the command explicit cleanups. Verify that the path being
+      // cleaned up is a sub-path of the script working directory. Fail if
+      // this is not the case.
+      //
+      for (const auto& cl: c.cleanups)
+      {
+        const path& p (cl.path);
+        path np (normalize (p, *env.work_dir.path, ll));
+
+        const string& ls (np.leaf ().string ());
+        bool wc (ls == "*" || ls == "**" || ls == "***");
+        const path& cp (wc ? np.directory () : np);
+        const dir_path* sd (env.sandbox_dir.path);
+
+        if (sd != nullptr && !cp.sub (*sd))
+          fail (ll) << (wc                ? "wildcard"  :
+                        p.to_directory () ? "directory" :
+                                            "file")
+                    << " cleanup " << p << " is out of "
+                    << diag_path (env.sandbox_dir);
+
+        env.clean ({cl.type, move (np)}, false);
+      }
+
+      bool eq (c.exit.comparison == exit_comparison::eq);
+
+      // If stdin file descriptor is not open then this is the first pipeline
+      // command.
+      //
+      bool first (ifd.get () == -1);
+
+      command_pipe::const_iterator nc (bc + 1);
+      bool last (nc == ec);
+
+      const string& program (c.program.string ());
+
+      const redirect& in ((c.in ? *c.in : env.in).effective ());
+
+      const redirect* out (!last
+                           ? nullptr // stdout is piped.
+                           : &(c.out ? *c.out : env.out).effective ());
+
+      const redirect& err ((c.err ? *c.err : env.err).effective ());
+
+      auto process_args = [&c] () -> cstrings
+      {
+        cstrings args {c.program.string ().c_str ()};
+
+        for (const auto& a: c.arguments)
+          args.push_back (a.c_str ());
+
+        args.push_back (nullptr);
+        return args;
+      };
+
+      // Prior to opening file descriptors for command input/output
+      // redirects let's check if the command is the exit builtin. Being a
+      // builtin syntactically it differs from the regular ones in a number
+      // of ways. It doesn't communicate with standard streams, so
+      // redirecting them is meaningless. It may appear only as a single
+      // command in a pipeline. It doesn't return any value and stops the
+      // script execution, so checking its exit status is meaningless as
+      // well. That all means we can short-circuit here calling the builtin
+      // and bailing out right after that. Checking that the user didn't
+      // specify any redirects or exit code check sounds like a right thing
+      // to do.
+      //
+      if (program == "exit")
+      {
+        // In case the builtin is erroneously pipelined from the other
+        // command, we will close stdin gracefully (reading out the stream
+        // content), to make sure that the command doesn't print any
+        // unwanted diagnostics about IO operation failure.
+        //
+        // Note that dtor will ignore any errors (which is what we want).
+        //
+        ifdstream is (move (ifd), fdstream_mode::skip);
+
+        if (!first || !last)
+          fail (ll) << "exit builtin must be the only pipe command";
+
+        if (c.in)
+          fail (ll) << "exit builtin stdin cannot be redirected";
+
+        if (c.out)
+          fail (ll) << "exit builtin stdout cannot be redirected";
+
+        if (c.err)
+          fail (ll) << "exit builtin stderr cannot be redirected";
+
+        // We can't make sure that there is no exit code check. Let's, at
+        // least, check that non-zero code is not expected.
+        //
+        if (eq != (c.exit.code == 0))
+          fail (ll) << "exit builtin exit code cannot be non-zero";
+
+        if (verb >= 2)
+          print_process (process_args ());
+
+        exit_builtin (c.arguments, ll); // Throws exit exception.
+      }
+
+      // Create a unique path for a command standard stream cache file.
+      //
+      auto std_path = [&env, &ci, &li, &ll] (const char* n) -> path
+      {
+        using std::to_string;
+
+        path p (n);
+
+        // 0 if belongs to a single-line script, otherwise is the command line
+        // number (start from one) in the script.
+        //
+        if (li > 0)
+          p += "-" + to_string (li);
+
+        // 0 if belongs to a single-command expression, otherwise is the
+        // command number (start from one) in the expression.
+        //
+        // Note that the name like stdin-N can relate to N-th command of a
+        // single-line script or to N-th single-command line of multi-line
+        // script. These cases are mutually exclusive and so are unambiguous.
+        //
+        if (ci > 0)
+          p += "-" + to_string (ci);
+
+        return normalize (move (p), temp_dir (env), ll);
+      };
+
+      // If this is the first pipeline command, then open stdin descriptor
+      // according to the redirect specified.
+      //
+      path isp;
+
+      if (!first)
+        assert (!c.in); // No redirect expected.
+      else
+      {
+        // Open a file for passing to the command stdin.
+        //
+        auto open_stdin = [&isp, &ifd, &ll] ()
+        {
+          assert (!isp.empty ());
+
+          try
+          {
+            ifd = fdopen (isp, fdopen_mode::in);
+          }
+          catch (const io_error& e)
+          {
+            fail (ll) << "unable to read " << isp << ": " << e;
+          }
+        };
+
+        switch (in.type)
+        {
+        case redirect_type::pass:
+          {
+            try
+            {
+              ifd = fddup (0);
+            }
+            catch (const io_error& e)
+            {
+              fail (ll) << "unable to duplicate stdin: " << e;
+            }
+
+            break;
+          }
+        case redirect_type::none:
+          // Somehow need to make sure that the child process doesn't read
+          // from stdin. That is tricky to do in a portable way. Here we
+          // suppose that the program which (erroneously) tries to read some
+          // data from stdin being redirected to /dev/null fails not being
+          // able to read the expected data, and so the command doesn't pass
+          // through.
+          //
+          // @@ Obviously doesn't cover the case when the process reads
+          //    whatever available.
+          // @@ Another approach could be not to redirect stdin and let the
+          //    process to hang which can be interpreted as a command failure.
+          // @@ Both ways are quite ugly. Is there some better way to do
+          //    this?
+          //
+          // Fall through.
+          //
+        case redirect_type::null:
+          {
+            ifd = open_null ();
+            break;
+          }
+        case redirect_type::file:
+          {
+            isp = normalize (in.file.path, *env.work_dir.path, ll);
+
+            open_stdin ();
+            break;
+          }
+        case redirect_type::here_str_literal:
+        case redirect_type::here_doc_literal:
+          {
+            // We could write to the command stdin directly but instead will
+            // cache the data for potential troubleshooting.
+            //
+            isp = std_path ("stdin");
+
+            save (isp,
+                  transform (in.str, false /* regex */, in.modifiers (), env),
+                  ll);
+
+            env.clean_special (isp);
+
+            open_stdin ();
+            break;
+          }
+        case redirect_type::trace:
+        case redirect_type::merge:
+        case redirect_type::here_str_regex:
+        case redirect_type::here_doc_regex:
+        case redirect_type::here_doc_ref:   assert (false); break;
+        }
+      }
+
+      assert (ifd.get () != -1);
+
+      // Prior to opening file descriptors for command outputs redirects
+      // let's check if the command is the set builtin. Being a builtin
+      // syntactically it differs from the regular ones in a number of ways.
+      // It either succeeds or terminates abnormally, so redirecting stderr
+      // is meaningless. It also never produces any output and may appear
+      // only as a terminal command in a pipeline. That means we can
+      // short-circuit here calling the builtin and returning right after
+      // that. Checking that the user didn't specify any meaningless
+      // redirects or exit code check sounds as a right thing to do.
+      //
+      if (program == "set")
+      {
+        if (!last)
+          fail (ll) << "set builtin must be the last pipe command";
+
+        if (c.out)
+          fail (ll) << "set builtin stdout cannot be redirected";
+
+        if (c.err)
+          fail (ll) << "set builtin stderr cannot be redirected";
+
+        if (eq != (c.exit.code == 0))
+          fail (ll) << "set builtin exit code cannot be non-zero";
+
+        if (verb >= 2)
+          print_process (process_args ());
+
+        set_builtin (env, c.arguments, move (ifd), ll);
+        return true;
+      }
+
+      // Open a file for command output redirect if requested explicitly
+      // (file overwrite/append redirects) or for the purpose of the output
+      // validation (none, here_*, file comparison redirects), register the
+      // file for cleanup, return the file descriptor. Interpret trace
+      // redirect according to the verbosity level (as null if below 2, as
+      // pass otherwise). Return nullfd, standard stream descriptor duplicate
+      // or null-device descriptor for merge, pass or null redirects
+      // respectively (not opening any file).
+      //
+      auto open = [&env, &ll, &std_path] (const redirect& r,
+                                          int dfd,
+                                          path& p) -> auto_fd
+      {
+        assert (dfd == 1 || dfd == 2);
+        const char* what (dfd == 1 ? "stdout" : "stderr");
+
+        fdopen_mode m (fdopen_mode::out | fdopen_mode::create);
+
+        redirect_type rt (r.type != redirect_type::trace
+                          ? r.type
+                          : verb < 2
+                          ? redirect_type::null
+                          : redirect_type::pass);
+        switch (rt)
+        {
+        case redirect_type::pass:
+          {
+            try
+            {
+              return fddup (dfd);
+            }
+            catch (const io_error& e)
+            {
+              fail (ll) << "unable to duplicate " << what << ": " << e;
+            }
+          }
+
+        case redirect_type::null: return open_null ();
+
+          // Duplicate the paired file descriptor later.
+          //
+        case redirect_type::merge: return nullfd;
+
+        case redirect_type::file:
+          {
+            // For the cmp mode the user-provided path refers a content to
+            // match against, rather than a content to be produced (as for
+            // overwrite and append modes). And so for cmp mode we redirect
+            // the process output to a temporary file.
+            //
+            p = r.file.mode == redirect_fmode::compare
+              ? std_path (what)
+              : normalize (r.file.path, *env.work_dir.path, ll);
+
+            m |= r.file.mode == redirect_fmode::append
+              ? fdopen_mode::at_end
+              : fdopen_mode::truncate;
+
+            break;
+          }
+
+        case redirect_type::none:
+        case redirect_type::here_str_literal:
+        case redirect_type::here_doc_literal:
+        case redirect_type::here_str_regex:
+        case redirect_type::here_doc_regex:
+          {
+            p = std_path (what);
+            m |= fdopen_mode::truncate;
+            break;
+          }
+
+        case redirect_type::trace:
+        case redirect_type::here_doc_ref: assert (false); break;
+        }
+
+        auto_fd fd;
+
+        try
+        {
+          fd = fdopen (p, m);
+
+          if ((m & fdopen_mode::at_end) != fdopen_mode::at_end)
+          {
+            if (rt == redirect_type::file)
+              env.clean ({cleanup_type::always, p}, true);
+            else
+              env.clean_special (p);
+          }
+        }
+        catch (const io_error& e)
+        {
+          fail (ll) << "unable to write to " << p << ": " << e;
+        }
+
+        return fd;
+      };
+
+      path osp;
+      fdpipe ofd;
+
+      // If this is the last command in the pipeline than redirect the
+      // command process stdout to a file. Otherwise create a pipe and
+      // redirect the stdout to the write-end of the pipe. The read-end will
+      // be passed as stdin for the next command in the pipeline.
+      //
+      // @@ Shouldn't we allow the here-* and file output redirects for a
+      //    command with pipelined output? Say if such redirect is present
+      //    then the process output is redirected to a file first (as it is
+      //    when no output pipelined), and only after the process exit code
+      //    and the output are validated the next command in the pipeline is
+      //    executed taking the file as an input. This could be usefull for
+      //    script failures investigation and, for example, for validation
+      //    "tightening".
+      //
+      if (last)
+        ofd.out = open (*out, 1, osp);
+      else
+      {
+        assert (!c.out); // No redirect expected.
+        ofd = open_pipe ();
+      }
+
+      path esp;
+      auto_fd efd (open (err, 2, esp));
+
+      // Merge standard streams.
+      //
+      bool mo (out != nullptr && out->type == redirect_type::merge);
+      if (mo || err.type == redirect_type::merge)
+      {
+        auto_fd& self  (mo ? ofd.out : efd);
+        auto_fd& other (mo ? efd : ofd.out);
+
+        try
+        {
+          assert (self.get () == -1 && other.get () != -1);
+          self = fddup (other.get ());
+        }
+        catch (const io_error& e)
+        {
+          fail (ll) << "unable to duplicate " << (mo ? "stderr" : "stdout")
+                    << ": " << e;
+        }
+      }
+
+      // All descriptors should be open to the date.
+      //
+      assert (ofd.out.get () != -1 && efd.get () != -1);
+
+      optional<process_exit> exit;
+      builtin_function* bf (builtins.find (program));
+
+      bool success;
+
+      if (bf != nullptr)
+      {
+        // Execute the builtin.
+        //
+        if (verb >= 2)
+          print_process (process_args ());
+
+        // Some of the script builtins (cp, mkdir, etc) extend libbutl
+        // builtins (via callbacks) registering/moving cleanups for the
+        // filesystem entries they create/move, unless explicitly requested
+        // not to do so via the --no-cleanup option.
+        //
+        // Let's "wrap up" the cleanup-related flags into the single object
+        // to rely on "small function object" optimization.
+        //
+        struct cleanup
+        {
+          // Whether the cleanups are enabled for the builtin. Can be set to
+          // false by the parse_option callback if --no-cleanup is
+          // encountered.
+          //
+          bool enabled = true;
+
+          // Whether to register cleanup for a filesystem entry being
+          // created/updated depending on its existence. Calculated by the
+          // create pre-hook and used by the subsequent post-hook.
+          //
+          bool add;
+
+          // Whether to move existing cleanups for the filesystem entry
+          // being moved, rather than to erase them. Calculated by the move
+          // pre-hook and used by the subsequent post-hook.
+          //
+          bool move;
+        };
+
+        // nullopt if the builtin doesn't support cleanups.
+        //
+        optional<cleanup> cln;
+
+        if (cleanup_builtin (program))
+          cln = cleanup ();
+
+        builtin_callbacks bcs {
+
+          // create
+          //
+          // Unless cleanups are suppressed, test that the filesystem entry
+          // doesn't exist (pre-hook) and, if that's the case, register the
+          // cleanup for the newly created filesystem entry (post-hook).
+          //
+          [&env, &cln] (const path& p, bool pre)
+          {
+            // Cleanups must be supported by a filesystem entry-creating
+            // builtin.
+            //
+            assert (cln);
+
+            if (cln->enabled)
+            {
+              if (pre)
+                cln->add = !butl::entry_exists (p);
+              else if (cln->add)
+                env.clean ({cleanup_type::always, p}, true /* implicit */);
+            }
+          },
+
+          // move
+          //
+          // Validate the source and destination paths (pre-hook) and,
+          // unless suppressed, adjust the cleanups that are sub-paths of
+          // the source path (post-hook).
+          //
+          [&env, &cln] (const path& from, const path& to, bool force, bool pre)
+          {
+            // Cleanups must be supported by a filesystem entry-moving
+            // builtin.
+            //
+            assert (cln);
+
+            if (pre)
+            {
+              const dir_path& wd (*env.work_dir.path);
+              const dir_path* sd (env.sandbox_dir.path);
+
+              auto fail = [] (const string& d) {throw runtime_error (d);};
+
+              if (sd != nullptr && !from.sub (*sd) && !force)
+                fail (diag_path (from) + " is out of " +
+                      diag_path (env.sandbox_dir));
+
+              auto check_wd = [&wd, &env, fail] (const path& p)
+              {
+                if (wd.sub (path_cast<dir_path> (p)))
+                  fail (diag_path (p) + " contains " +
+                        diag_path (env.work_dir));
+              };
+
+              check_wd (from);
+              check_wd (to);
+
+              // Unless cleanups are disabled, "move" the matching cleanups
+              // if the destination path doesn't exist and it is a sub-path
+              // of the working directory and just remove them otherwise.
+              //
+              if (cln->enabled)
+                cln->move = !butl::entry_exists (to) &&
+                            (sd == nullptr || to.sub (*sd));
+            }
+            else if (cln->enabled)
+            {
+              // Move or remove the matching cleanups (see above).
+              //
+              // Note that it's not enough to just change the cleanup paths.
+              // We also need to make sure that these cleanups happen before
+              // the destination directory (or any of its parents) cleanup,
+              // that is potentially registered. To achieve that we can just
+              // relocate these cleanup entries to the end of the list,
+              // preserving their mutual order. Remember that cleanups in
+              // the list are executed in the reversed order.
+              //
+              cleanups cs;
+
+              // Remove the source path sub-path cleanups from the list,
+              // adjusting/caching them if required (see above).
+              //
+              for (auto i (env.cleanups.begin ()); i != env.cleanups.end (); )
+              {
+                script::cleanup& c (*i);
+                path& p (c.path);
+
+                if (p.sub (from))
+                {
+                  if (cln->move)
+                  {
+                    // Note that we need to preserve the cleanup path
+                    // trailing separator which indicates the removal
+                    // method. Also note that leaf(), in particular, does
+                    // that.
+                    //
+                    p = p != from
+                      ? to / p.leaf (path_cast<dir_path> (from))
+                      : p.to_directory ()
+                        ? path_cast<dir_path> (to)
+                        : to;
+
+                    cs.push_back (move (c));
+                  }
+
+                  i = env.cleanups.erase (i);
+                }
+                else
+                  ++i;
+              }
+
+              // Re-insert the adjusted cleanups at the end of the list.
+              //
+              env.cleanups.insert (env.cleanups.end (),
+                                   make_move_iterator (cs.begin ()),
+                                   make_move_iterator (cs.end ()));
+
+            }
+          },
+
+          // remove
+          //
+          // Validate the filesystem entry path (pre-hook).
+          //
+          [&env] (const path& p, bool force, bool pre)
+          {
+            if (pre)
+            {
+              const dir_path& wd (*env.work_dir.path);
+              const dir_path* sd (env.sandbox_dir.path);
+
+              auto fail = [] (const string& d) {throw runtime_error (d);};
+
+              if (sd != nullptr && !p.sub (*sd) && !force)
+                fail (diag_path (p) + " is out of " +
+                      diag_path (env.sandbox_dir));
+
+              if (wd.sub (path_cast<dir_path> (p)))
+                fail (diag_path (p) + " contains " +
+                      diag_path (env.work_dir));
+            }
+          },
+
+          // parse_option
+          //
+          [&cln] (const strings& args, size_t i)
+          {
+            // Parse --no-cleanup, if it is supported by the builtin.
+            //
+            if (cln && args[i] == "--no-cleanup")
+            {
+              cln->enabled = false;
+              return 1;
+            }
+
+            return 0;
+          },
+
+          // sleep
+          //
+          // Deactivate the thread before going to sleep.
+          //
+          [&env] (const duration& d)
+          {
+            // If/when required we could probably support the precise sleep
+            // mode (e.g., via an option).
+            //
+            env.context.sched.sleep (d);
+          }
+        };
+
+        try
+        {
+          uint8_t r; // Storage.
+          builtin b (bf (r,
+                         c.arguments,
+                         move (ifd), move (ofd.out), move (efd),
+                         *env.work_dir.path,
+                         bcs));
+
+          success = run_pipe (env,
+                              nc,
+                              ec,
+                              move (ofd.in),
+                              ci + 1, li, ll, diag);
+
+          exit = process_exit (b.wait ());
+        }
+        catch (const system_error& e)
+        {
+          fail (ll) << "unable to execute " << c.program << " builtin: "
+                    << e << endf;
+        }
+      }
+      else
+      {
+        // Execute the process.
+        //
+        cstrings args (process_args ());
+
+        // Resolve the relative not simple program path against the script's
+        // working directory. The simple one will be left for the process
+        // path search machinery. Also strip the potential leading `^`,
+        // indicating that this is an external program rather than a
+        // builtin.
+        //
+        path p;
+
+        try
+        {
+          p = path (args[0]);
+
+          if (p.relative ())
+          {
+            auto program = [&p, &args] (path pp)
+            {
+              p = move (pp);
+              args[0] = p.string ().c_str ();
+            };
+
+            if (p.simple ())
+            {
+              const string& s (p.string ());
+
+              // Don't end up with an empty path.
+              //
+              if (s.size () > 1 && s[0] == '^')
+                program (path (s, 1, s.size () - 1));
+            }
+            else
+              program (*env.work_dir.path / p);
+          }
+        }
+        catch (const invalid_path& e)
+        {
+          fail (ll) << "invalid program path " << e.path;
+        }
+
+        try
+        {
+          process_path pp (process::path_search (args[0]));
+
+          // Note: the builtin-escaping character '^' is not printed.
+          //
+          if (verb >= 2)
+            print_process (args);
+
+          process pr (
+            pp,
+            args.data (),
+            {ifd.get (), -1}, process::pipe (ofd), {-1, efd.get ()},
+            env.work_dir.path->string ().c_str ());
+
+          ifd.reset ();
+          ofd.out.reset ();
+          efd.reset ();
+
+          success = run_pipe (env,
+                              nc,
+                              ec,
+                              move (ofd.in),
+                              ci + 1, li, ll, diag);
+
+          pr.wait ();
+
+          exit = move (pr.exit);
+        }
+        catch (const process_error& e)
+        {
+          error (ll) << "unable to execute " << args[0] << ": " << e;
+
+          if (e.child)
+            std::exit (1);
+
+          throw failed ();
+        }
+      }
+
+      assert (exit);
+
+      // If the righ-hand side pipeline failed than the whole pipeline fails,
+      // and no further checks are required.
+      //
+      if (!success)
+        return false;
+
+      const path& pr (c.program);
+
+      // If there is no valid exit code available by whatever reason then we
+      // print the proper diagnostics, dump stderr (if cached and not too
+      // large) and fail the whole script. Otherwise if the exit code is not
+      // correct then we print diagnostics if requested and fail the
+      // pipeline.
+      //
+      bool valid (exit->normal ());
+
+      // On Windows the exit code can be out of the valid codes range being
+      // defined as uint16_t.
+      //
+#ifdef _WIN32
+      if (valid)
+        valid = exit->code () < 256;
+#endif
+
+      success = valid && eq == (exit->code () == c.exit.code);
+
+      if (!valid || (!success && diag))
+      {
+        // In the presense of a valid exit code we print the diagnostics and
+        // return false rather than throw.
+        //
+        diag_record d (valid ? error (ll) : fail (ll));
+
+        if (!exit->normal ())
+          d << pr << " " << *exit;
+        else
+        {
+          uint16_t ec (exit->code ()); // Make sure is printed as integer.
+
+          if (!valid)
+            d << pr << " exit code " << ec << " out of 0-255 range";
+          else if (!success)
+          {
+            if (diag)
+              d << pr << " exit code " << ec << (eq ? " != " : " == ")
+                << static_cast<uint16_t> (c.exit.code);
+          }
+          else
+            assert (false);
+        }
+
+        if (non_empty (esp, ll) && avail_on_failure (esp, env))
+          d << info << "stderr: " << esp;
+
+        if (non_empty (osp, ll) && avail_on_failure (osp, env))
+          d << info << "stdout: " << osp;
+
+        if (non_empty (isp, ll) && avail_on_failure (isp, env))
+          d << info << "stdin: " << isp;
+
+        // Print cached stderr.
+        //
+        print_file (d, esp, ll);
+      }
+
+      // If exit code is correct then check if the standard outputs match the
+      // expectations. Note that stdout is only redirected to file for the
+      // last command in the pipeline.
+      //
+      // The thinking behind matching stderr first is that if it mismatches,
+      // then the program probably misbehaves (executes wrong functionality,
+      // etc) in which case its stdout doesn't really matter.
+      //
+      if (success)
+        success =
+          check_output (pr, esp, isp, err, ll, env, diag, "stderr") &&
+          (!last ||
+           check_output (pr, osp, isp, *out, ll, env, diag, "stdout"));
+
+      return success;
+    }
+
+    static bool
+    run_expr (environment& env,
+              const command_expr& expr,
+              size_t li, const location& ll,
+              bool diag)
+    {
+      // Commands are numbered sequentially throughout the expression
+      // starting with 1. Number 0 means the command is a single one.
+      //
+      size_t ci (expr.size () == 1 && expr.back ().pipe.size () == 1
+                 ? 0
+                 : 1);
+
+      // If there is no ORs to the right of a pipe then the pipe failure is
+      // fatal for the whole expression. In particular, the pipe must print
+      // the diagnostics on failure (if generally allowed). So we find the
+      // pipe that "switches on" the diagnostics potential printing.
+      //
+      command_expr::const_iterator trailing_ands; // Undefined if diag is
+      // disallowed.
+      if (diag)
+      {
+        auto i (expr.crbegin ());
+        for (; i != expr.crend () && i->op == expr_operator::log_and; ++i) ;
+        trailing_ands = i.base ();
+      }
+
+      bool r (false);
+      bool print (false);
+
+      for (auto b (expr.cbegin ()), i (b), e (expr.cend ()); i != e; ++i)
+      {
+        if (diag && i + 1 == trailing_ands)
+          print = true;
+
+        const command_pipe& p (i->pipe);
+        bool or_op (i->op == expr_operator::log_or);
+
+        // Short-circuit if the pipe result must be OR-ed with true or AND-ed
+        // with false.
+        //
+        if (!((or_op && r) || (!or_op && !r)))
+          r = run_pipe (
+            env, p.begin (), p.end (), auto_fd (), ci, li, ll, print);
+
+        ci += p.size ();
+      }
+
+      return r;
+    }
+
+    void
+    run (environment& env,
+         const command_expr& expr,
+         size_t li, const location& ll)
+    {
+      // Note that we don't print the expression at any verbosity level
+      // assuming that the caller does this, potentially providing some
+      // additional information (command type, etc).
+      //
+      if (!run_expr (env, expr, li, ll, true /* diag */))
+        throw failed (); // Assume diagnostics is already printed.
+    }
+
+    bool
+    run_if (environment& env,
+            const command_expr& expr,
+            size_t li, const location& ll)
+    {
+      // Note that we don't print the expression here (see above).
+      //
+      return run_expr (env, expr, li, ll, false /* diag */);
+    }
+
+    void
+    clean (environment& env, const location& ll)
+    {
+      context& ctx (env.context);
+      const dir_path& wdir (*env.work_dir.path);
+
+      // Note that we operate with normalized paths here.
+      //
+      // Remove special files. The order is not important as we don't
+      // expect directories here.
+      //
+      for (const path& p: env.special_cleanups)
+      {
+        // Remove the file if exists. Fail otherwise.
+        //
+        if (rmfile (ctx, p, 3) == rmfile_status::not_exist)
+          fail (ll) << "registered for cleanup special file " << p
+                    << " does not exist";
+      }
+
+      // Remove files and directories in the order opposite to the order of
+      // cleanup registration.
+      //
+      for (const auto& c: reverse_iterate (env.cleanups))
+      {
+        cleanup_type t (c.type);
+
+        // Skip whenever the path exists or not.
+        //
+        if (t == cleanup_type::never)
+          continue;
+
+        const path& cp (c.path);
+
+        // Wildcard with the last component being '***' (without trailing
+        // separator) matches all files and sub-directories recursively as
+        // well as the start directories itself. So we will recursively
+        // remove the directories that match the parent (for the original
+        // path) directory wildcard.
+        //
+        bool recursive (cp.leaf ().representation () == "***");
+        const path& p (!recursive ? cp : cp.directory ());
+
+        // Remove files or directories using wildcard.
+        //
+        if (path_pattern (p))
+        {
+          bool removed (false);
+
+          auto rm = [&cp, recursive, &removed, &ll, &ctx, &wdir]
+                    (path&& pe, const string&, bool interm)
+          {
+            if (!interm)
+            {
+              // While removing the entry we can get not_exist due to
+              // racing conditions, but that's ok if somebody did our job.
+              // Note that we still set the removed flag to true in this
+              // case.
+              //
+              removed = true; // Will be meaningless on failure.
+
+              if (pe.to_directory ())
+              {
+                dir_path d (path_cast<dir_path> (pe));
+
+                if (!recursive)
+                {
+                  rmdir_status r (rmdir (ctx, d, 3));
+
+                  if (r != rmdir_status::not_empty)
+                    return true;
+
+                  diag_record dr (fail (ll));
+                  dr << "registered for cleanup directory " << d
+                     << " is not empty";
+
+                  print_dir (dr, d, ll);
+                  dr << info << "wildcard: '" << cp << "'";
+                }
+                else
+                {
+                  // Don't remove the working directory (it will be removed
+                  // by the dedicated cleanup).
+                  //
+                  // Cast to uint16_t to avoid ambiguity with
+                  // libbutl::rmdir_r().
+                  //
+                  rmdir_status r (rmdir_r (ctx, d, d != wdir, 3));
+
+                  if (r != rmdir_status::not_empty)
+                    return true;
+
+                  // The directory is unlikely to be current but let's keep
+                  // for completeness.
+                  //
+                  fail (ll) << "registered for cleanup wildcard " << cp
+                            << " matches the current directory";
+                }
+              }
+              else
+                rmfile (ctx, pe, 3);
+            }
+
+            return true;
+          };
+
+          // Note that here we rely on the fact that recursive iterating
+          // goes depth-first (which make sense for the cleanup).
+          //
+          try
+          {
+            // Doesn't follow symlinks.
+            //
+            path_search (p,
+                         rm,
+                         dir_path () /* start */,
+                         path_match_flags::none);
+          }
+          catch (const system_error& e)
+          {
+            fail (ll) << "unable to cleanup wildcard " << cp << ": " << e;
+          }
+
+          // Removal of no filesystem entries is not an error for 'maybe'
+          // cleanup type.
+          //
+          if (removed || t == cleanup_type::maybe)
+            continue;
+
+          fail (ll) << "registered for cleanup wildcard " << cp
+                    << " doesn't match any "
+                    << (recursive
+                        ? "path"
+                        : p.to_directory ()
+                        ? "directory"
+                        : "file");
+        }
+
+        // Remove the directory if exists and empty. Fail otherwise.
+        // Removal of non-existing directory is not an error for 'maybe'
+        // cleanup type.
+        //
+        if (p.to_directory ())
+        {
+          dir_path d (path_cast<dir_path> (p));
+          bool wd (d == wdir);
+
+          // Don't remove the working directory for the recursive cleanup
+          // (it will be removed by the dedicated one).
+          //
+          // Note that the root working directory contains the
+          // .buildignore file (see above).
+          //
+          // @@ If 'd' is a file then will fail with a diagnostics having
+          //    no location info. Probably need to add an optional location
+          //    parameter to rmdir() function. The same problem exists for
+          //    a file cleanup when try to rmfile() directory instead of
+          //    file.
+          //
+          rmdir_status r (recursive
+                          ? rmdir_r (ctx, d, !wd, static_cast <uint16_t> (3))
+                          : rmdir (ctx, d, 3));
+
+          if (r == rmdir_status::success ||
+              (r == rmdir_status::not_exist && t == cleanup_type::maybe))
+            continue;
+
+          diag_record dr (fail (ll));
+          dr << "registered for cleanup directory " << d
+             << (r == rmdir_status::not_exist ? " does not exist" :
+                 !recursive                   ? " is not empty"
+                                              : " is current");
+
+          if (r == rmdir_status::not_empty)
+            print_dir (dr, d, ll);
+        }
+
+        // Remove the file if exists. Fail otherwise. Removal of
+        // non-existing file is not an error for 'maybe' cleanup type.
+        //
+        if (rmfile (ctx, p, 3) == rmfile_status::not_exist &&
+            t == cleanup_type::always)
+          fail (ll) << "registered for cleanup file " << p
+                    << " does not exist";
+      }
+    }
+
+    void
+    print_dir (diag_record& dr, const dir_path& p, const location& ll)
+    {
+      try
+      {
+        size_t n (0);
+        for (const dir_entry& de: dir_iterator (p,
+                                                false /* ignore_dangling */))
+        {
+          if (n++ < 10)
+            dr << '\n' << (de.ltype () == entry_type::directory
+                           ? path_cast<dir_path> (de.path ())
+                           : de.path ());
+        }
+
+        if (n > 10)
+          dr << "\nand " << n - 10 << " more file(s)";
+      }
+      catch (const system_error& e)
+      {
+        fail (ll) << "unable to iterate over " << p << ": " << e;
+      }
+    }
+  }
+}
diff --git a/libbuild2/script/run.hxx b/libbuild2/script/run.hxx
new file mode 100644
index 0000000..477dd88
--- /dev/null
+++ b/libbuild2/script/run.hxx
@@ -0,0 +1,75 @@
+// file      : libbuild2/script/run.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_SCRIPT_RUN_HXX
+#define LIBBUILD2_SCRIPT_RUN_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/script/script.hxx>
+
+namespace build2
+{
+  namespace script
+  {
+    // An exception that can be thrown by an expression running function to
+    // exit the script (for example, as a result of executing the exit builtin
+    // by the below run*() functions). The status indicates whether the
+    // execution should be considered to have succeeded or failed.
+    //
+    struct exit
+    {
+      bool status;
+
+      explicit
+      exit (bool s): status (s) {}
+    };
+
+    // Helpers.
+    //
+
+    // Command expression running functions.
+    //
+    // Index is the 1-base index of this command line in the command list.
+    // If it is 0 then it means there is only one command. This information
+    // can be used, for example, to derive file names.
+    //
+    // Location is the start position of this command line in the script. It
+    // can be used in diagnostics.
+    //
+    void
+    run (environment&, const command_expr&, size_t index, const location&);
+
+    bool
+    run_if (environment&, const command_expr&, size_t, const location&);
+
+    // Perform the registered special file cleanups in the direct order and
+    // then the regular cleanups in the reverse order.
+    //
+    void
+    clean (environment&, const location&);
+
+    // Print first 10 directory sub-entries to the diag record. The directory
+    // must exist. Is normally used while issuing diagnostics on non-empty
+    // directory removal failure.
+    //
+    void
+    print_dir (diag_record&, const dir_path&, const location&);
+
+    // Return the quoted path representation with the preserved trailing
+    // directory separator. The path is relative if the verbosity level is
+    // less than 3.
+    //
+    string
+    diag_path (const path&);
+
+    // Same as above, but prepends the path with a name, if present. The path
+    // must be not NULL.
+    //
+    string
+    diag_path (const dir_name_view&);
+  }
+}
+
+#endif // LIBBUILD2_SCRIPT_RUN_HXX
diff --git a/libbuild2/script/script.cxx b/libbuild2/script/script.cxx
new file mode 100644
index 0000000..c85bfd3
--- /dev/null
+++ b/libbuild2/script/script.cxx
@@ -0,0 +1,659 @@
+// file      : libbuild2/script/script.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/script/script.hxx>
+
+#include <sstream>
+#include <cstring> // strchr()
+
+using namespace std;
+
+namespace build2
+{
+  namespace script
+  {
+    ostream&
+    operator<< (ostream& o, line_type lt)
+    {
+      const char* s (nullptr);
+
+      switch (lt)
+      {
+      case line_type::var:       s = "variable"; break;
+      case line_type::cmd:       s = "command";  break;
+      case line_type::cmd_if:    s = "'if'";     break;
+      case line_type::cmd_ifn:   s = "'if!'";    break;
+      case line_type::cmd_elif:  s = "'elif'";   break;
+      case line_type::cmd_elifn: s = "'elif!'";  break;
+      case line_type::cmd_else:  s = "'else'";   break;
+      case line_type::cmd_end:   s = "'end'";    break;
+      }
+
+      return o << s;
+    }
+
+    void
+    dump (ostream& os, const string& ind, const lines& ls)
+    {
+      // For each line print its tokens literal representation trying to
+      // reproduce the quoting. Consider mixed quoting as double quoting
+      // since the information is lost.
+      //
+      // Also additionally indent the if-branch lines.
+      //
+      string if_ind;
+
+      for (const line& l: ls)
+      {
+        // Before printing indentation, decrease it if the else or end line is
+        // reached.
+        //
+        switch (l.type)
+        {
+        case line_type::cmd_elif:
+        case line_type::cmd_elifn:
+        case line_type::cmd_else:
+        case line_type::cmd_end:
+          {
+            size_t n (if_ind.size ());
+            assert (n >= 2);
+            if_ind.resize (n - 2);
+            break;
+          }
+        default: break;
+        }
+
+        // Print indentations.
+        //
+        os << ind << if_ind;
+
+        // After printing indentation, increase it for if/else branch.
+        //
+        switch (l.type)
+        {
+        case line_type::cmd_if:
+        case line_type::cmd_ifn:
+        case line_type::cmd_elif:
+        case line_type::cmd_elifn:
+        case line_type::cmd_else:  if_ind += "  "; break;
+        default: break;
+        }
+
+        // '"' or '\'' if we are inside the quoted token sequence and '\0'
+        // otherwise. Thus, can be used as bool.
+        //
+        char qseq ('\0');
+
+        for (const replay_token& rt: l.tokens)
+        {
+          const token& t (rt.token);
+
+          // '"' or '\'' if the token is quoted and '\0' otherwise. Thus,
+          // can be used as bool.
+          //
+          char qtok ('\0');
+
+          switch (t.qtype)
+          {
+          case quote_type::unquoted: qtok = '\0'; break;
+          case quote_type::single:   qtok = '\''; break;
+          case quote_type::mixed:
+          case quote_type::double_:  qtok = '"';  break;
+          }
+
+          // If being inside a quoted token sequence we have reached a token
+          // quoted differently or the newline, then we probably made a
+          // mistake misinterpreting some previous partially quoted token, for
+          // example f"oo" as "foo. If that's the case, all we can do is to
+          // end the sequence adding the trailing quote.
+          //
+          // Note that a token inside the quoted sequence may well be
+          // unquoted, so for example "$foo" is lexed as:
+          //
+          //   token  quoting  complete  notes
+          //   ''     "        no
+          //   $      "        yes
+          //   'foo'                     Unquoted since lexed in variable mode.
+          //   ''     "        no
+          //   \n
+          //
+          if (qseq &&
+              ((qtok && qtok != qseq) || t.type == token_type::newline))
+          {
+            os << qseq;
+            qseq = '\0';
+          }
+
+          // Left and right token quotes (can be used as bool).
+          //
+          char lq ('\0');
+          char rq ('\0');
+
+          // If the token is quoted, then determine if/which quotes should be
+          // present on its sides and track the quoted token sequence.
+          //
+          if (qtok)
+          {
+            if (t.qcomp) // Complete token quoting.
+            {
+              // If we are inside a quoted token sequence then do noting.
+              // Otherwise just quote the current token not starting a
+              // sequence.
+              //
+              if (!qseq)
+              {
+                lq = qtok;
+                rq = qtok;
+              }
+            }
+            else         // Partial token quoting.
+            {
+              // Note that we can not always reproduce the original tokens
+              // representation for partial quoting. For example, the two
+              // following tokens are lexed into the identical token objects:
+              //
+              // "foo
+              // f"oo"
+              //
+              // We will always assume that the partially quoted token either
+              // starts or ends the quoted token sequence. Sometimes this ends
+              // up unexpectedly, but seems there is not much we can do:
+              //
+              // f"oo" "ba"r  ->  "foo bar"
+              //
+              if (!qseq)     // Start quoted sequence.
+              {
+                lq = qtok;
+                qseq = qtok;
+              }
+              else           // End quoted sequence.
+              {
+                rq = qtok;
+                qseq = '\0';
+              }
+            }
+          }
+
+          // Print the space character prior to the separated token, unless
+          // it is a first like token or the newline.
+          //
+          if (t.separated                   &&
+              t.type != token_type::newline &&
+              &rt != &l.tokens[0])
+            os << ' ';
+
+          if (lq) os << lq; // Print the left quote, if required.
+
+          // Escape the special characters, unless the token in not a word or
+          // is single-quoted. Note that the special character set depends on
+          // whether the word is double-quoted or unquoted.
+          //
+          if (t.type == token_type::word && qtok != '\'')
+          {
+            for (char c: t.value)
+            {
+              if (strchr (qtok ? "\\\"" : "|&<>=\\\"", c) != nullptr)
+                os << '\\';
+
+              os << c;
+            }
+          }
+          else
+            t.printer (os, t, print_mode::raw);
+
+          if (rq) os << rq; // Print the right quote, if required.
+        }
+      }
+    }
+
+    // Quote if empty or contains spaces or any of the special characters.
+    // Note that we use single quotes since double quotes still allow
+    // expansion.
+    //
+    // @@ What if it contains single quotes?
+    //
+    static void
+    to_stream_q (ostream& o, const string& s)
+    {
+      if (s.empty () || s.find_first_of (" |&<>=\\\"") != string::npos)
+        o << '\'' << s << '\'';
+      else
+        o << s;
+    };
+
+    void
+    to_stream (ostream& o, const command& c, command_to_stream m)
+    {
+      auto print_path = [&o] (const path& p)
+      {
+        using build2::operator<<;
+
+        ostringstream s;
+        stream_verb (s, stream_verb (o));
+        s << p;
+
+        to_stream_q (o, s.str ());
+      };
+
+      auto print_redirect = [&o, print_path] (const redirect& r, int fd)
+      {
+        const redirect& er (r.effective ());
+
+        // Print the none redirect (no data allowed) if/when the respective
+        // syntax is invented.
+        //
+        if (er.type == redirect_type::none)
+          return;
+
+        o << ' ';
+
+        // Print the redirect file descriptor.
+        //
+        if (fd == 2)
+          o << fd;
+
+        // Print the redirect original representation and the modifiers, if
+        // present.
+        //
+        r.token.printer (o, r.token, print_mode::raw);
+
+        // Print the rest of the redirect (file path, etc).
+        //
+        switch (er.type)
+        {
+        case redirect_type::none:         assert (false); break;
+        case redirect_type::here_doc_ref: assert (false); break;
+
+        case redirect_type::pass:
+        case redirect_type::null:
+        case redirect_type::trace:             break;
+        case redirect_type::merge: o << er.fd; break;
+
+        case redirect_type::file:
+          {
+            print_path (er.file.path);
+            break;
+          }
+
+        case redirect_type::here_str_literal:
+        case redirect_type::here_doc_literal:
+          {
+            if (er.type == redirect_type::here_doc_literal)
+              o << er.end;
+            else
+            {
+              const string& v (er.str);
+              to_stream_q (o,
+                           er.modifiers ().find (':') == string::npos
+                           ? string (v, 0, v.size () - 1) // Strip newline.
+                           : v);
+            }
+
+            break;
+          }
+
+        case redirect_type::here_str_regex:
+        case redirect_type::here_doc_regex:
+          {
+            const regex_lines& re (er.regex);
+
+            if (er.type == redirect_type::here_doc_regex)
+              o << re.intro + er.end + re.intro + re.flags;
+            else
+            {
+              assert (!re.lines.empty ()); // Regex can't be empty.
+
+              regex_line l (re.lines[0]);
+              to_stream_q (o, re.intro + l.value + re.intro + l.flags);
+            }
+
+            break;
+          }
+        }
+      };
+
+      auto print_doc = [&o] (const redirect& r)
+      {
+        o << endl;
+
+        if (r.type == redirect_type::here_doc_literal)
+          o << r.str;
+        else
+        {
+          assert (r.type == redirect_type::here_doc_regex);
+
+          const regex_lines& rl (r.regex);
+
+          for (auto b (rl.lines.cbegin ()), i (b), e (rl.lines.cend ());
+               i != e; ++i)
+          {
+            if (i != b)
+              o << endl;
+
+            const regex_line& l (*i);
+
+            if (l.regex)                  // Regex (possibly empty),
+              o << rl.intro << l.value << rl.intro << l.flags;
+            else if (!l.special.empty ()) // Special literal.
+              o << rl.intro;
+            else                          // Textual literal.
+              o << l.value;
+
+            o << l.special;
+          }
+        }
+
+        o << (r.modifiers ().find (':') == string::npos ? "" : "\n") << r.end;
+      };
+
+      if ((m & command_to_stream::header) == command_to_stream::header)
+      {
+        // Program.
+        //
+        to_stream_q (o, c.program.string ());
+
+        // Arguments.
+        //
+        for (const string& a: c.arguments)
+        {
+          o << ' ';
+          to_stream_q (o, a);
+        }
+
+        // Redirects.
+        //
+        if (c.in)
+          print_redirect (*c.in, 0);
+
+        if (c.out)
+          print_redirect (*c.out, 1);
+
+        if (c.err)
+          print_redirect (*c.err, 2);
+
+        for (const auto& p: c.cleanups)
+        {
+          o << " &";
+
+          if (p.type != cleanup_type::always)
+            o << (p.type == cleanup_type::maybe ? '?' : '!');
+
+          print_path (p.path);
+        }
+
+        if (c.exit.comparison != exit_comparison::eq || c.exit.code != 0)
+        {
+          switch (c.exit.comparison)
+          {
+          case exit_comparison::eq: o << " == "; break;
+          case exit_comparison::ne: o << " != "; break;
+          }
+
+          o << static_cast<uint16_t> (c.exit.code);
+        }
+      }
+
+      if ((m & command_to_stream::here_doc) == command_to_stream::here_doc)
+      {
+        // Here-documents.
+        //
+        if (c.in &&
+            (c.in->type == redirect_type::here_doc_literal ||
+             c.in->type == redirect_type::here_doc_regex))
+          print_doc (*c.in);
+
+        if (c.out &&
+            (c.out->type == redirect_type::here_doc_literal ||
+             c.out->type == redirect_type::here_doc_regex))
+          print_doc (*c.out);
+
+        if (c.err &&
+            (c.err->type == redirect_type::here_doc_literal ||
+             c.err->type == redirect_type::here_doc_regex))
+          print_doc (*c.err);
+      }
+    }
+
+    void
+    to_stream (ostream& o, const command_pipe& p, command_to_stream m)
+    {
+      if ((m & command_to_stream::header) == command_to_stream::header)
+      {
+        for (auto b (p.begin ()), i (b); i != p.end (); ++i)
+        {
+          if (i != b)
+            o << " | ";
+
+          to_stream (o, *i, command_to_stream::header);
+        }
+      }
+
+      if ((m & command_to_stream::here_doc) == command_to_stream::here_doc)
+      {
+        for (const command& c: p)
+          to_stream (o, c, command_to_stream::here_doc);
+      }
+    }
+
+    void
+    to_stream (ostream& o, const command_expr& e, command_to_stream m)
+    {
+      if ((m & command_to_stream::header) == command_to_stream::header)
+      {
+        for (auto b (e.begin ()), i (b); i != e.end (); ++i)
+        {
+          if (i != b)
+          {
+            switch (i->op)
+            {
+            case expr_operator::log_or:  o << " || "; break;
+            case expr_operator::log_and: o << " && "; break;
+            }
+          }
+
+          to_stream (o, i->pipe, command_to_stream::header);
+        }
+      }
+
+      if ((m & command_to_stream::here_doc) == command_to_stream::here_doc)
+      {
+        for (const expr_term& t: e)
+          to_stream (o, t.pipe, command_to_stream::here_doc);
+      }
+    }
+
+    // redirect
+    //
+    redirect::
+    redirect (redirect_type t)
+        : type (t)
+    {
+      switch (type)
+      {
+      case redirect_type::none:
+      case redirect_type::pass:
+      case redirect_type::null:
+      case redirect_type::trace:
+      case redirect_type::merge: break;
+
+      case redirect_type::here_str_literal:
+      case redirect_type::here_doc_literal: new (&str) string (); break;
+
+      case redirect_type::here_str_regex:
+      case redirect_type::here_doc_regex:
+        {
+          new (&regex) regex_lines ();
+          break;
+        }
+
+      case redirect_type::file: new (&file) file_type (); break;
+
+      case redirect_type::here_doc_ref: assert (false); break;
+      }
+    }
+
+    redirect::
+    redirect (redirect&& r) noexcept
+        : type (r.type),
+          token (move (r.token)),
+          end (move (r.end)),
+          end_line (r.end_line),
+          end_column (r.end_column)
+    {
+      switch (type)
+      {
+      case redirect_type::none:
+      case redirect_type::pass:
+      case redirect_type::null:
+      case redirect_type::trace: break;
+
+      case redirect_type::merge: fd = r.fd; break;
+
+      case redirect_type::here_str_literal:
+      case redirect_type::here_doc_literal:
+        {
+          new (&str) string (move (r.str));
+          break;
+        }
+      case redirect_type::here_str_regex:
+      case redirect_type::here_doc_regex:
+        {
+          new (&regex) regex_lines (move (r.regex));
+          break;
+        }
+      case redirect_type::file:
+        {
+          new (&file) file_type (move (r.file));
+          break;
+        }
+      case redirect_type::here_doc_ref:
+        {
+          new (&ref) reference_wrapper<const redirect> (r.ref);
+          break;
+        }
+      }
+    }
+
+    redirect& redirect::
+    operator= (redirect&& r) noexcept
+    {
+      if (this != &r)
+      {
+        this->~redirect ();
+        new (this) redirect (move (r)); // Assume noexcept move-constructor.
+      }
+      return *this;
+    }
+
+    redirect::
+    ~redirect ()
+    {
+      switch (type)
+      {
+      case redirect_type::none:
+      case redirect_type::pass:
+      case redirect_type::null:
+      case redirect_type::trace:
+      case redirect_type::merge: break;
+
+      case redirect_type::here_str_literal:
+      case redirect_type::here_doc_literal: str.~string (); break;
+
+      case redirect_type::here_str_regex:
+      case redirect_type::here_doc_regex: regex.~regex_lines (); break;
+
+      case redirect_type::file: file.~file_type (); break;
+
+      case redirect_type::here_doc_ref:
+        {
+          ref.~reference_wrapper<const redirect> ();
+          break;
+        }
+      }
+    }
+
+    redirect::
+    redirect (const redirect& r)
+        : type (r.type),
+          token (r.token),
+          end (r.end),
+          end_line (r.end_line),
+          end_column (r.end_column)
+    {
+      switch (type)
+      {
+      case redirect_type::none:
+      case redirect_type::pass:
+      case redirect_type::null:
+      case redirect_type::trace: break;
+
+      case redirect_type::merge: fd = r.fd; break;
+
+      case redirect_type::here_str_literal:
+      case redirect_type::here_doc_literal:
+        {
+          new (&str) string (r.str);
+          break;
+        }
+      case redirect_type::here_str_regex:
+      case redirect_type::here_doc_regex:
+        {
+          new (&regex) regex_lines (r.regex);
+          break;
+        }
+      case redirect_type::file:
+        {
+          new (&file) file_type (r.file);
+          break;
+        }
+      case redirect_type::here_doc_ref:
+        {
+          new (&ref) reference_wrapper<const redirect> (r.ref);
+          break;
+        }
+      }
+    }
+
+    redirect& redirect::
+    operator= (const redirect& r)
+    {
+      if (this != &r)
+        *this = redirect (r); // Reduce to move-assignment.
+      return *this;
+    }
+
+    // environment
+    //
+    void environment::
+    clean (script::cleanup c, bool implicit)
+    {
+      using script::cleanup;
+
+      assert (!implicit || c.type == cleanup_type::always);
+
+      const path& p (c.path);
+
+      if (sandbox_dir.path != nullptr && !p.sub (*sandbox_dir.path))
+      {
+        if (implicit)
+          return;
+        else
+          assert (false); // Error so should have been checked.
+      }
+
+      auto pr = [&p] (const cleanup& v) -> bool {return v.path == p;};
+      auto i (find_if (cleanups.begin (), cleanups.end (), pr));
+
+      if (i == cleanups.end ())
+        cleanups.emplace_back (move (c));
+      else if (!implicit)
+        i->type = c.type;
+    }
+
+    void environment::
+    clean_special (path p)
+    {
+      special_cleanups.emplace_back (move (p));
+    }
+  }
+}
diff --git a/libbuild2/script/script.hxx b/libbuild2/script/script.hxx
new file mode 100644
index 0000000..f4998b7
--- /dev/null
+++ b/libbuild2/script/script.hxx
@@ -0,0 +1,471 @@
+// file      : libbuild2/script/script.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_SCRIPT_SCRIPT_HXX
+#define LIBBUILD2_SCRIPT_SCRIPT_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/forward.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/token.hxx>
+#include <libbuild2/variable.hxx>
+
+namespace build2
+{
+  namespace script
+  {
+    // Pre-parsed representation.
+    //
+
+    enum class line_type
+    {
+      var,
+      cmd,
+      cmd_if,
+      cmd_ifn,
+      cmd_elif,
+      cmd_elifn,
+      cmd_else,
+      cmd_end
+    };
+
+    ostream&
+    operator<< (ostream&, line_type);
+
+    struct line
+    {
+      line_type type;
+      replay_tokens tokens;
+
+      union
+      {
+        const variable* var; // Pre-entered for line_type::var.
+      };
+    };
+
+    // Most of the time we will have just one line (a command).
+    //
+    using lines = small_vector<line, 1>;
+
+    // Print the script lines, trying to reproduce their original (non-
+    // expanded) representation.
+    //
+    // Note that the exact spacing and partial quoting may not be restored due
+    // to the information loss.
+    //
+    void
+    dump (ostream&, const string& ind, const lines&);
+
+    // Parse object model.
+    //
+
+    // redirect
+    //
+    enum class redirect_type
+    {
+      // No data is allowed to be read or written.
+      //
+      // Note that redirect of this type cannot be currently specified on the
+      // script command line and can only be set via the environment object
+      // as a default redirect (see below).
+      //
+      none,
+
+      pass,
+      null,
+      trace,
+      merge,
+      here_str_literal,
+      here_str_regex,
+      here_doc_literal,
+      here_doc_regex,
+      here_doc_ref,     // Reference to here_doc literal or regex.
+      file,
+    };
+
+    // Pre-parsed (but not instantiated) regex lines. The idea here is that
+    // we should be able to re-create their (more or less) exact text
+    // representation for diagnostics but also instantiate without any
+    // re-parsing.
+    //
+    struct regex_line
+    {
+      // If regex is true, then value is the regex expression. Otherwise, it
+      // is a literal. Note that special characters can be present in both
+      // cases. For example, //+ is a regex, while /+ is a literal, both
+      // with '+' as a special character. Flags are only valid for regex.
+      // Literals falls apart into textual (has no special characters) and
+      // special (has just special characters instead) ones. For example
+      // foo is a textual literal, while /.+ is a special one. Note that
+      // literal must not have value and special both non-empty.
+      //
+      bool regex;
+
+      string value;
+      string flags;
+      string special;
+
+      uint64_t line;
+      uint64_t column;
+
+      // Create regex with optional special characters.
+      //
+      regex_line (uint64_t l, uint64_t c,
+                  string v, string f, string s = string ())
+          : regex (true),
+            value (move (v)),
+            flags (move (f)),
+            special (move (s)),
+            line (l),
+            column (c) {}
+
+      // Create a literal, either text or special.
+      //
+      regex_line (uint64_t l, uint64_t c, string v, bool s)
+          : regex (false),
+            value (s ? string () : move (v)),
+            special (s ? move (v) : string ()),
+            line (l),
+            column (c) {}
+    };
+
+    struct regex_lines
+    {
+      char intro;   // Introducer character.
+      string flags; // Global flags (here-document).
+
+      small_vector<regex_line, 8> lines;
+    };
+
+    // Output file redirect mode.
+    //
+    enum class redirect_fmode
+    {
+      compare,
+      overwrite,
+      append
+    };
+
+    struct redirect
+    {
+      redirect_type type;
+
+      struct file_type
+      {
+        using path_type = build2::path;
+        path_type path;
+        redirect_fmode mode; // Meaningless for input redirect.
+      };
+
+      union
+      {
+        int         fd;    // Merge-to descriptor.
+        string      str;   // Note: with trailing newline, if requested.
+        regex_lines regex; // Note: with trailing blank, if requested.
+        file_type   file;
+        reference_wrapper<const redirect> ref; // Note: no chains.
+      };
+
+      // Modifiers and the original representation (potentially an alias).
+      //
+      build2::token token;
+
+      string end;         // Here-document end marker (no regex intro/flags).
+      uint64_t end_line;  // Here-document end marker location.
+      uint64_t end_column;
+
+      // Create redirect of a type other than reference.
+      //
+      explicit
+      redirect (redirect_type);
+
+      // Create redirect of the reference type.
+      //
+      redirect (redirect_type t, const redirect& r, build2::token tk)
+          : type (redirect_type::here_doc_ref),
+            ref (r),
+            token (move (tk))
+      {
+        // There is no support (and need) for reference chains.
+        //
+        assert (t == redirect_type::here_doc_ref &&
+                r.type != redirect_type::here_doc_ref);
+      }
+
+      // Create redirect of the merge type.
+      //
+      // Note that it's the caller's responsibility to make sure that the file
+      // descriptor is valid for this redirect (2 for stdout, etc).
+      //
+      redirect (redirect_type t, int f)
+          : type (redirect_type::merge), fd (f)
+      {
+        assert (t == redirect_type::merge && (f == 1 || f == 2));
+      }
+
+      redirect (redirect&&) noexcept;
+      redirect& operator= (redirect&&) noexcept;
+
+      // @@ Defining optional movable-only redirects in the command class make
+      // the older C++ compilers (GCC 4.9, Clang 4, VC 15) fail to compile the
+      // command vector manipulating code. Thus, we make the redirect class
+      // copyable to workaround the issue.
+      //
+      redirect (const redirect&);
+      redirect& operator= (const redirect&);
+
+      ~redirect ();
+
+      const redirect&
+      effective () const noexcept
+      {
+        return type == redirect_type::here_doc_ref ? ref.get () : *this;
+      }
+
+      const string&
+      modifiers () const noexcept
+      {
+        return token.value;
+      }
+    };
+
+    // cleanup
+    //
+    enum class cleanup_type
+    {
+      always, // &foo  - cleanup, fail if does not exist.
+      maybe,  // &?foo - cleanup, ignore if does not exist.
+      never   // &!foo - don’t cleanup, ignore if doesn’t exist.
+    };
+
+    // File or directory to be automatically cleaned up at the end of the
+    // script execution. If the path ends with a trailing slash, then it is
+    // assumed to be a directory, otherwise -- a file. A directory that is
+    // about to be cleaned up must be empty.
+    //
+    // The last component in the path may contain a wildcard that have the
+    // following semantics:
+    //
+    // dir/*   - remove all immediate files
+    // dir/*/  - remove all immediate sub-directories (must be empty)
+    // dir/**  - remove all files recursively
+    // dir/**/ - remove all sub-directories recursively (must be empty)
+    // dir/*** - remove directory dir with all files and sub-directories
+    //           recursively
+    //
+    struct cleanup
+    {
+      cleanup_type type;
+      build2::path path;
+    };
+    using cleanups = vector<cleanup>;
+
+    // command_exit
+    //
+    enum class exit_comparison {eq, ne};
+
+    struct command_exit
+    {
+      // C/C++ don't apply constraints on program exit code other than it
+      // being of type int.
+      //
+      // POSIX specifies that only the least significant 8 bits shall be
+      // available from wait() and waitpid(); the full value shall be
+      // available from waitid() (read more at _Exit, _exit Open Group
+      // spec).
+      //
+      // While the Linux man page for waitid() doesn't mention any
+      // deviations from the standard, the FreeBSD implementation (as of
+      // version 11.0) only returns 8 bits like the other wait*() calls.
+      //
+      // Windows supports 32-bit exit codes.
+      //
+      // Note that in shells some exit values can have special meaning so
+      // using them can be a source of confusion. For bash values in the
+      // [126, 255] range are such a special ones (see Appendix E, "Exit
+      // Codes With Special Meanings" in the Advanced Bash-Scripting Guide).
+      //
+      exit_comparison comparison;
+      uint8_t code;
+    };
+
+    // command
+    //
+    struct command
+    {
+      path program;
+      strings arguments;
+
+      optional<redirect> in;
+      optional<redirect> out;
+      optional<redirect> err;
+
+      script::cleanups cleanups;
+
+      command_exit exit {exit_comparison::eq, 0};
+    };
+
+    enum class command_to_stream: uint16_t
+    {
+      header   = 0x01,
+      here_doc = 0x02,              // Note: printed on a new line.
+      all      = header | here_doc
+    };
+
+    void
+    to_stream (ostream&, const command&, command_to_stream);
+
+    ostream&
+    operator<< (ostream&, const command&);
+
+    // command_pipe
+    //
+    using command_pipe = vector<command>;
+
+    void
+    to_stream (ostream&, const command_pipe&, command_to_stream);
+
+    ostream&
+    operator<< (ostream&, const command_pipe&);
+
+    // command_expr
+    //
+    enum class expr_operator {log_or, log_and};
+
+    struct expr_term
+    {
+      expr_operator op;  // OR-ed to an implied false for the first term.
+      command_pipe pipe;
+    };
+
+    using command_expr = vector<expr_term>;
+
+    void
+    to_stream (ostream&, const command_expr&, command_to_stream);
+
+    ostream&
+    operator<< (ostream&, const command_expr&);
+
+    // Script execution environment.
+    //
+    class environment
+    {
+    public:
+      build2::context& context;
+
+      // The platform script programs run on.
+      //
+      const target_triplet& host;
+
+      // The work directory is used as the builtin/process CWD and to complete
+      // relative paths. Any attempt to remove or move this directory (or its
+      // parent directory) using the rm or mv builtins will fail. Must be an
+      // absolute path.
+      //
+      const dir_name_view work_dir;
+
+      // If the sanbox directory is not NULL, then any attempt to remove or
+      // move a filesystem entry outside this directory using an explicit
+      // cleanup or the rm/mv builtins will fail, unless the --force option is
+      // specified for the builtin. Must be an absolute path.
+      //
+      const dir_name_view sandbox_dir;
+
+      // The temporary directory is used by the script running machinery to
+      // create special files. Must be an absolute path, unless empty. Can be
+      // empty until the create_temp_dir() function call, which can be used
+      // for creating this directory on demand.
+      //
+      const dir_path& temp_dir;
+
+      // If true, the temporary directory will not be removed on the script
+      // failure. In particular, this allows the script running machinery to
+      // refer to the special files in diagnostics.
+      //
+      const bool temp_dir_keep;
+
+      // Default process streams redirects.
+      //
+      // If a stream redirect is not specified on the script command line,
+      // then the respective redirect data member will be used as the default.
+      //
+      const redirect in;
+      const redirect out;
+      const redirect err;
+
+      environment (build2::context& ctx,
+                   const target_triplet& h,
+                   const dir_name_view& wd,
+                   const dir_name_view& sd,
+                   const dir_path& td, bool tk,
+                   redirect&& i = redirect (redirect_type::pass),
+                   redirect&& o = redirect (redirect_type::pass),
+                   redirect&& e = redirect (redirect_type::pass))
+          : context (ctx), host (h),
+            work_dir (wd), sandbox_dir (sd), temp_dir (td), temp_dir_keep (tk),
+            in (move (i)), out (move (o)), err (move (e))
+      {
+      }
+
+      // Create environment without the sandbox.
+      //
+      environment (build2::context& ctx,
+                   const target_triplet& h,
+                   const dir_name_view& wd,
+                   const dir_path& td, bool tk,
+                   redirect&& i = redirect (redirect_type::pass),
+                   redirect&& o = redirect (redirect_type::pass),
+                   redirect&& e = redirect (redirect_type::pass))
+          : environment (ctx, h,
+                         wd, dir_name_view (), td, tk,
+                         move (i), move (o), move (e))
+      {
+      }
+
+      // Cleanup.
+      //
+    public:
+      script::cleanups cleanups;
+      paths special_cleanups;
+
+      // Register a cleanup. If the cleanup is explicit, then override the
+      // cleanup type if this path is already registered. Ignore implicit
+      // registration of a path outside root directory (see below).
+      //
+      void
+      clean (cleanup, bool implicit);
+
+      // Register cleanup of a special file. Such files are created to
+      // maintain the script running machinery and must be removed first, not
+      // to interfere with the user-defined wildcard cleanups if the working
+      // and temporary directories are the same.
+      //
+      void
+      clean_special (path);
+
+    public:
+      // Set variable value with optional (non-empty) attributes.
+      //
+      virtual void
+      set_variable (string&& name,
+                    names&&,
+                    const string& attrs,
+                    const location&) = 0;
+
+      // Create the temporary directory and set the temp_dir reference target
+      // to its path. Must only be called if temp_dir is empty.
+      //
+      virtual void
+      create_temp_dir () = 0;
+
+    public:
+      virtual
+      ~environment () = default;
+    };
+  }
+}
+
+#include <libbuild2/script/script.ixx>
+
+#endif // LIBBUILD2_SCRIPT_SCRIPT_HXX
diff --git a/libbuild2/script/script.ixx b/libbuild2/script/script.ixx
new file mode 100644
index 0000000..56043b2
--- /dev/null
+++ b/libbuild2/script/script.ixx
@@ -0,0 +1,56 @@
+// file      : libbuild2/script/script.ixx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+namespace build2
+{
+  namespace script
+  {
+    inline command_to_stream
+    operator&= (command_to_stream& x, command_to_stream y)
+    {
+      return x = static_cast<command_to_stream> (
+        static_cast<uint16_t> (x) & static_cast<uint16_t> (y));
+    }
+
+    inline command_to_stream
+    operator|= (command_to_stream& x, command_to_stream y)
+    {
+      return x = static_cast<command_to_stream> (
+        static_cast<uint16_t> (x) | static_cast<uint16_t> (y));
+    }
+
+    inline command_to_stream
+    operator& (command_to_stream x, command_to_stream y) {return x &= y;}
+
+    inline command_to_stream
+    operator| (command_to_stream x, command_to_stream y) {return x |= y;}
+
+
+    // command
+    //
+    inline ostream&
+    operator<< (ostream& o, const command& c)
+    {
+      to_stream (o, c, command_to_stream::all);
+      return o;
+    }
+
+    // command_pipe
+    //
+    inline ostream&
+    operator<< (ostream& o, const command_pipe& p)
+    {
+      to_stream (o, p, command_to_stream::all);
+      return o;
+    }
+
+    // command_expr
+    //
+    inline ostream&
+    operator<< (ostream& o, const command_expr& e)
+    {
+      to_stream (o, e, command_to_stream::all);
+      return o;
+    }
+  }
+}
diff --git a/libbuild2/script/token.cxx b/libbuild2/script/token.cxx
new file mode 100644
index 0000000..1c612a5
--- /dev/null
+++ b/libbuild2/script/token.cxx
@@ -0,0 +1,53 @@
+// file      : libbuild2/script/token.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/script/token.hxx>
+
+using namespace std;
+
+namespace build2
+{
+  namespace script
+  {
+    void
+    token_printer (ostream& os, const token& t, print_mode m)
+    {
+      const string& v (t.value);
+
+      // Only quote non-name tokens for diagnostics.
+      //
+      const char* q (m == print_mode::diagnostics ? "'" : "");
+
+      switch (t.type)
+      {
+      case token_type::clean:        os << q << '&'    << v << q; break;
+      case token_type::pipe:         os << q << '|'         << q; break;
+
+      case token_type::in_pass:      os << q << "<|"        << q; break;
+      case token_type::in_null:      os << q << "<-"        << q; break;
+      case token_type::in_file:      os << q << "<="        << q; break;
+      case token_type::in_doc:       os << q << "<<="  << v << q; break;
+      case token_type::in_str:       os << q << "<<<=" << v << q; break;
+
+      case token_type::out_pass:     os << q << ">|"        << q; break;
+      case token_type::out_null:     os << q << ">-"        << q; break;
+      case token_type::out_trace:    os << q << ">!"        << q; break;
+      case token_type::out_merge:    os << q << ">&"        << q; break;
+      case token_type::out_file_ovr: os << q << ">="        << q; break;
+      case token_type::out_file_app: os << q << ">+"        << q; break;
+      case token_type::out_file_cmp: os << q << ">?"        << q; break;
+      case token_type::out_doc:      os << q << ">>?"  << v << q; break;
+      case token_type::out_str:      os << q << ">>>?" << v << q; break;
+
+      case token_type::in_l:         os << q << '<'    << v << q; break;
+      case token_type::in_ll:        os << q << "<<"   << v << q; break;
+      case token_type::in_lll:       os << q << "<<<"  << v << q; break;
+      case token_type::out_g:        os << q << '>'    << v << q; break;
+      case token_type::out_gg:       os << q << ">>"   << v << q; break;
+      case token_type::out_ggg:      os << q << ">>>"  << v << q; break;
+
+      default: build2::token_printer (os, t, m);
+      }
+    }
+  }
+}
diff --git a/libbuild2/script/token.hxx b/libbuild2/script/token.hxx
new file mode 100644
index 0000000..0186bd9
--- /dev/null
+++ b/libbuild2/script/token.hxx
@@ -0,0 +1,66 @@
+// file      : libbuild2/script/token.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_SCRIPT_TOKEN_HXX
+#define LIBBUILD2_SCRIPT_TOKEN_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/token.hxx>
+
+namespace build2
+{
+  namespace script
+  {
+    struct token_type: build2::token_type
+    {
+      using base_type = build2::token_type;
+
+      enum
+      {
+        // NOTE: remember to update token_printer()!
+
+        pipe = base_type::value_next, // |
+        clean,                        // &{?!}     (modifiers in value)
+
+        in_pass,                      // <|
+        in_null,                      // <-
+        in_file,                      // <=
+        in_doc,                       // <<={:/}   (modifiers in value)
+        in_str,                       // <<<={:/}  (modifiers in value)
+
+        out_pass,                     // >|
+        out_null,                     // >-
+        out_trace,                    // >!
+        out_merge,                    // >&
+        out_file_ovr,                 // >=
+        out_file_app,                 // >+
+        out_file_cmp,                 // >?
+        out_doc,                      // >>?{:/~}  (modifiers in value)
+        out_str,                      // >>>?{:/~} (modifiers in value)
+
+        // The modifiers are in the token value, if the redirect the alias
+        // resolves to supports the modifiers.
+        //
+        in_l,                         // <
+        in_ll,                        // <<
+        in_lll,                       // <<<
+        out_g,                        // >
+        out_gg,                       // >>
+        out_ggg,                      // >>>
+
+        value_next
+      };
+
+      token_type () = default;
+      token_type (value_type v): base_type (v) {}
+      token_type (base_type v): base_type (v) {}
+    };
+
+    void
+    token_printer (ostream&, const token&, print_mode);
+  }
+}
+
+#endif // LIBBUILD2_SCRIPT_TOKEN_HXX