Add support for 'for' loop second (... | for x) and third (for x <...) forms in script

10 files changed, 1107 insertions, 235 deletions

diff --git a/libbuild2/script/builtin-options.cxx b/libbuild2/script/builtin-options.cxx
index 8e15ddd..9b4067b 100644
--- a/libbuild2/script/builtin-options.cxx
+++ b/libbuild2/script/builtin-options.cxx
@@ -1076,6 +1076,297 @@ namespace build2
 
       return r;
     }
+
+    // for_options
+    //
+
+    for_options::
+    for_options ()
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+    }
+
+    for_options::
+    for_options (int& argc,
+                 char** argv,
+                 bool erase,
+                 ::build2::build::cli::unknown_mode opt,
+                 ::build2::build::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::build::cli::argv_scanner s (argc, argv, erase);
+      _parse (s, opt, arg);
+    }
+
+    for_options::
+    for_options (int start,
+                 int& argc,
+                 char** argv,
+                 bool erase,
+                 ::build2::build::cli::unknown_mode opt,
+                 ::build2::build::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::build::cli::argv_scanner s (start, argc, argv, erase);
+      _parse (s, opt, arg);
+    }
+
+    for_options::
+    for_options (int& argc,
+                 char** argv,
+                 int& end,
+                 bool erase,
+                 ::build2::build::cli::unknown_mode opt,
+                 ::build2::build::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::build::cli::argv_scanner s (argc, argv, erase);
+      _parse (s, opt, arg);
+      end = s.end ();
+    }
+
+    for_options::
+    for_options (int start,
+                 int& argc,
+                 char** argv,
+                 int& end,
+                 bool erase,
+                 ::build2::build::cli::unknown_mode opt,
+                 ::build2::build::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      ::build2::build::cli::argv_scanner s (start, argc, argv, erase);
+      _parse (s, opt, arg);
+      end = s.end ();
+    }
+
+    for_options::
+    for_options (::build2::build::cli::scanner& s,
+                 ::build2::build::cli::unknown_mode opt,
+                 ::build2::build::cli::unknown_mode arg)
+    : exact_ (),
+      newline_ (),
+      whitespace_ ()
+    {
+      _parse (s, opt, arg);
+    }
+
+    typedef
+    std::map<std::string, void (*) (for_options&, ::build2::build::cli::scanner&)>
+    _cli_for_options_map;
+
+    static _cli_for_options_map _cli_for_options_map_;
+
+    struct _cli_for_options_map_init
+    {
+      _cli_for_options_map_init ()
+      {
+        _cli_for_options_map_["--exact"] =
+        &::build2::build::cli::thunk< for_options, &for_options::exact_ >;
+        _cli_for_options_map_["-e"] =
+        &::build2::build::cli::thunk< for_options, &for_options::exact_ >;
+        _cli_for_options_map_["--newline"] =
+        &::build2::build::cli::thunk< for_options, &for_options::newline_ >;
+        _cli_for_options_map_["-n"] =
+        &::build2::build::cli::thunk< for_options, &for_options::newline_ >;
+        _cli_for_options_map_["--whitespace"] =
+        &::build2::build::cli::thunk< for_options, &for_options::whitespace_ >;
+        _cli_for_options_map_["-w"] =
+        &::build2::build::cli::thunk< for_options, &for_options::whitespace_ >;
+      }
+    };
+
+    static _cli_for_options_map_init _cli_for_options_map_init_;
+
+    bool for_options::
+    _parse (const char* o, ::build2::build::cli::scanner& s)
+    {
+      _cli_for_options_map::const_iterator i (_cli_for_options_map_.find (o));
+
+      if (i != _cli_for_options_map_.end ())
+      {
+        (*(i->second)) (*this, s);
+        return true;
+      }
+
+      return false;
+    }
+
+    bool for_options::
+    _parse (::build2::build::cli::scanner& s,
+            ::build2::build::cli::unknown_mode opt_mode,
+            ::build2::build::cli::unknown_mode arg_mode)
+    {
+      // Can't skip combined flags (--no-combined-flags).
+      //
+      assert (opt_mode != ::build2::build::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::build::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::build::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::build::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::build::cli::unknown_mode::skip:
+              {
+                s.skip ();
+                r = true;
+                continue;
+              }
+              case ::build2::build::cli::unknown_mode::stop:
+              {
+                break;
+              }
+              case ::build2::build::cli::unknown_mode::fail:
+              {
+                throw ::build2::build::cli::unknown_option (o);
+              }
+            }
+
+            break;
+          }
+        }
+
+        switch (arg_mode)
+        {
+          case ::build2::build::cli::unknown_mode::skip:
+          {
+            s.skip ();
+            r = true;
+            continue;
+          }
+          case ::build2::build::cli::unknown_mode::stop:
+          {
+            break;
+          }
+          case ::build2::build::cli::unknown_mode::fail:
+          {
+            throw ::build2::build::cli::unknown_argument (o);
+          }
+        }
+
+        break;
+      }
+
+      return r;
+    }
   }
 }
 
diff --git a/libbuild2/script/builtin-options.hxx b/libbuild2/script/builtin-options.hxx
index c7cebbc..9361d18 100644
--- a/libbuild2/script/builtin-options.hxx
+++ b/libbuild2/script/builtin-options.hxx
@@ -253,6 +253,90 @@ namespace build2
       vector<string> clear_;
       bool clear_specified_;
     };
+
+    class for_options
+    {
+      public:
+      for_options ();
+
+      for_options (int& argc,
+                   char** argv,
+                   bool erase = false,
+                   ::build2::build::cli::unknown_mode option = ::build2::build::cli::unknown_mode::fail,
+                   ::build2::build::cli::unknown_mode argument = ::build2::build::cli::unknown_mode::stop);
+
+      for_options (int start,
+                   int& argc,
+                   char** argv,
+                   bool erase = false,
+                   ::build2::build::cli::unknown_mode option = ::build2::build::cli::unknown_mode::fail,
+                   ::build2::build::cli::unknown_mode argument = ::build2::build::cli::unknown_mode::stop);
+
+      for_options (int& argc,
+                   char** argv,
+                   int& end,
+                   bool erase = false,
+                   ::build2::build::cli::unknown_mode option = ::build2::build::cli::unknown_mode::fail,
+                   ::build2::build::cli::unknown_mode argument = ::build2::build::cli::unknown_mode::stop);
+
+      for_options (int start,
+                   int& argc,
+                   char** argv,
+                   int& end,
+                   bool erase = false,
+                   ::build2::build::cli::unknown_mode option = ::build2::build::cli::unknown_mode::fail,
+                   ::build2::build::cli::unknown_mode argument = ::build2::build::cli::unknown_mode::stop);
+
+      for_options (::build2::build::cli::scanner&,
+                   ::build2::build::cli::unknown_mode option = ::build2::build::cli::unknown_mode::fail,
+                   ::build2::build::cli::unknown_mode argument = ::build2::build::cli::unknown_mode::stop);
+
+      // Option accessors and modifiers.
+      //
+      const bool&
+      exact () const;
+
+      bool&
+      exact ();
+
+      void
+      exact (const bool&);
+
+      const bool&
+      newline () const;
+
+      bool&
+      newline ();
+
+      void
+      newline (const bool&);
+
+      const bool&
+      whitespace () const;
+
+      bool&
+      whitespace ();
+
+      void
+      whitespace (const bool&);
+
+      // Implementation details.
+      //
+      protected:
+      bool
+      _parse (const char*, ::build2::build::cli::scanner&);
+
+      private:
+      bool
+      _parse (::build2::build::cli::scanner&,
+              ::build2::build::cli::unknown_mode option,
+              ::build2::build::cli::unknown_mode argument);
+
+      public:
+      bool exact_;
+      bool newline_;
+      bool whitespace_;
+    };
   }
 }
 
diff --git a/libbuild2/script/builtin-options.ixx b/libbuild2/script/builtin-options.ixx
index 8f84177..575eb95 100644
--- a/libbuild2/script/builtin-options.ixx
+++ b/libbuild2/script/builtin-options.ixx
@@ -153,6 +153,63 @@ namespace build2
     {
       this->clear_specified_ = x;
     }
+
+    // for_options
+    //
+
+    inline const bool& for_options::
+    exact () const
+    {
+      return this->exact_;
+    }
+
+    inline bool& for_options::
+    exact ()
+    {
+      return this->exact_;
+    }
+
+    inline void for_options::
+    exact (const bool& x)
+    {
+      this->exact_ = x;
+    }
+
+    inline const bool& for_options::
+    newline () const
+    {
+      return this->newline_;
+    }
+
+    inline bool& for_options::
+    newline ()
+    {
+      return this->newline_;
+    }
+
+    inline void for_options::
+    newline (const bool& x)
+    {
+      this->newline_ = x;
+    }
+
+    inline const bool& for_options::
+    whitespace () const
+    {
+      return this->whitespace_;
+    }
+
+    inline bool& for_options::
+    whitespace ()
+    {
+      return this->whitespace_;
+    }
+
+    inline void for_options::
+    whitespace (const bool& x)
+    {
+      this->whitespace_ = x;
+    }
   }
 }
 
diff --git a/libbuild2/script/builtin.cli b/libbuild2/script/builtin.cli
index 50dd3a0..c993983 100644
--- a/libbuild2/script/builtin.cli
+++ b/libbuild2/script/builtin.cli
@@ -30,5 +30,12 @@ namespace build2
       vector<string> --unset|-u;
       vector<string> --clear|-c;
     };
+
+    class for_options
+    {
+      bool --exact|-e;
+      bool --newline|-n;
+      bool --whitespace|-w;
+    };
   }
 }
diff --git a/libbuild2/script/parser.cxx b/libbuild2/script/parser.cxx
index 536821b..7989c20 100644
--- a/libbuild2/script/parser.cxx
+++ b/libbuild2/script/parser.cxx
@@ -4,10 +4,13 @@
 #include <libbuild2/script/parser.hxx>
 
 #include <cstring> // strchr()
+#include <sstream>
 
 #include <libbuild2/variable.hxx>
-#include <libbuild2/script/run.hxx>   // exit
+
+#include <libbuild2/script/run.hxx>             // exit, stream_reader
 #include <libbuild2/script/lexer.hxx>
+#include <libbuild2/script/builtin-options.hxx>
 
 using namespace std;
 
@@ -140,18 +143,20 @@ namespace build2
       return nullopt;
     }
 
-    pair<command_expr, parser::here_docs> parser::
+    parser::parse_command_expr_result parser::
     parse_command_expr (token& t, type& tt,
-                        const redirect_aliases& ra)
+                        const redirect_aliases& ra,
+                        optional<token>&& program)
     {
-      // enter: first token of the command line
+      // enter: first (or second, if program) 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 ()});
+      if (!pre_parse_)
+        expr.push_back ({expr_operator::log_or, command_pipe ()});
 
       command c; // Command being assembled.
 
@@ -218,8 +223,8 @@ namespace build2
       // 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_word = [&c, &p, &mod, &check_regex_mod, this]
+                      (string&& w, const location& l)
       {
         auto add_merge = [&l, this] (optional<redirect>& r,
                                      const string& w,
@@ -697,11 +702,30 @@ namespace build2
       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).
+      // "terminators" (newline or unknown/unexpected token).
       //
       location l (ll);
       names ns; // Reuse to reduce allocations.
 
+      bool for_loop (false);
+
+      if (program)
+      {
+        assert (program->type == type::word);
+
+        // Note that here we skip all the parse_program() business since the
+        // program can only be one of the specially-recognized names.
+        //
+        if (program->value == "for")
+          for_loop = true;
+        else
+          assert (false); // Must be specially-recognized program.
+
+        // Save the program name and continue parsing as a command.
+        //
+        add_word (move (program->value), get_location (*program));
+      }
+
       for (bool done (false); !done; l = get_location (t))
       {
         tt = ra.resolve (tt);
@@ -717,6 +741,9 @@ namespace build2
         case type::equal:
         case type::not_equal:
           {
+            if (for_loop)
+              fail (l) << "for-loop exit code cannot be checked";
+
             if (!pre_parse_)
               check_pending (l);
 
@@ -747,30 +774,39 @@ namespace build2
           }
 
         case type::pipe:
+          if (for_loop)
+            fail (l) << "for-loop must be last command in a pipe";
+          // Fall through.
+
         case type::log_or:
         case type::log_and:
+          if (for_loop)
+            fail (l) << "command expression involving for-loop";
+          // Fall through.
 
-        case type::in_pass:
-        case type::out_pass:
+        case type::clean:
+          if (for_loop)
+            fail (l) << "cleanup in for-loop";
+          // Fall through.
 
-        case type::in_null:
+        case type::out_pass:
         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:
+          if (for_loop)
+            fail (l) << "output redirect in for-loop";
+          // Fall through.
 
-        case type::clean:
+        case type::in_pass:
+        case type::in_null:
+        case type::in_str:
+        case type::in_doc:
+        case type::in_file:
           {
             if (pre_parse_)
             {
@@ -968,6 +1004,42 @@ namespace build2
             next (t, tt);
             break;
           }
+        case type::lsbrace:
+          {
+            // Recompose the attributes into a single command argument.
+            //
+            assert (!pre_parse_);
+
+            attributes_push (t, tt, true /* standalone */);
+
+            attributes as (attributes_pop ());
+            assert (!as.empty ());
+
+            ostringstream os;
+            names storage;
+            char c ('[');
+            for (const attribute& a: as)
+            {
+              os << c << a.name;
+
+              if (!a.value.null)
+              {
+                os << '=';
+
+                storage.clear ();
+                to_stream (os,
+                           reverse (a.value, storage),
+                           quote_mode::normal,
+                           '@');
+              }
+
+              c = ',';
+            }
+            os << ']';
+
+            add_word (os.str (), l);
+            break;
+          }
         default:
           {
             // Bail out if this is one of the unknown tokens.
@@ -1053,16 +1125,33 @@ namespace build2
             bool prog (p == pending::program_first ||
                        p == pending::program_next);
 
-            // Check if this is the env pseudo-builtin.
+            // Check if this is the env pseudo-builtin or the for-loop.
             //
             bool env (false);
-            if (prog && tt == type::word && t.value == "env")
+            if (prog && tt == type::word)
             {
-              parsed_env r (parse_env_builtin (t, tt));
-              c.cwd       = move (r.cwd);
-              c.variables = move (r.variables);
-              c.timeout   = r.timeout;
-              env = true;
+              if (t.value == "env")
+              {
+                parsed_env r (parse_env_builtin (t, tt));
+                c.cwd       = move (r.cwd);
+                c.variables = move (r.variables);
+                c.timeout   = r.timeout;
+                env = true;
+              }
+              else if (t.value == "for")
+              {
+                if (expr.size () > 1)
+                  fail (l) << "command expression involving for-loop";
+
+                for_loop = true;
+
+                // Save 'for' as a program name and continue parsing as a
+                // command.
+                //
+                add_word (move (t.value), l);
+                next (t, tt);
+                continue;
+              }
             }
 
             // Parse the next chunk as names to get expansion, etc. Note that
@@ -1243,9 +1332,16 @@ namespace build2
                   switch (tt)
                   {
                   case type::pipe:
+                    if (for_loop)
+                      fail (l) << "for-loop must be last command in a pipe";
+                    // Fall through.
+
                   case type::log_or:
                   case type::log_and:
                     {
+                      if (for_loop)
+                        fail (l) << "command expression involving for-loop";
+
                       // Check that the previous command makes sense.
                       //
                       check_command (l, tt != type::pipe);
@@ -1265,30 +1361,11 @@ namespace build2
                       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:
                     {
+                      if (for_loop)
+                        fail (l) << "cleanup in for-loop";
+
                       parse_clean (t);
                       break;
                     }
@@ -1299,6 +1376,27 @@ namespace build2
                       fail (l) << "here-document redirect in expansion";
                       break;
                     }
+
+                  case type::out_pass:
+                  case type::out_null:
+                  case type::out_trace:
+                  case type::out_merge:
+                  case type::out_str:
+                  case type::out_file_cmp:
+                  case type::out_file_ovr:
+                  case type::out_file_app:
+                    if (for_loop)
+                      fail (l) << "output redirect in for-loop";
+                    // Fall through.
+
+                  case type::in_pass:
+                  case type::in_null:
+                  case type::in_str:
+                  case type::in_file:
+                    {
+                      parse_redirect (move (t), tt, l);
+                      break;
+                    }
                   }
                 }
 
@@ -1326,7 +1424,7 @@ namespace build2
         expr.back ().pipe.push_back (move (c));
       }
 
-      return make_pair (move (expr), move (hd));
+      return parse_command_expr_result {move (expr), move (hd), for_loop};
     }
 
     parser::parsed_env parser::
@@ -1575,7 +1673,7 @@ namespace build2
 
     void parser::
     parse_here_documents (token& t, type& tt,
-                          pair<command_expr, here_docs>& p)
+                          parse_command_expr_result& pr)
     {
       // enter: newline
       // leave: newline
@@ -1583,7 +1681,7 @@ namespace build2
       // Parse here-document fragments in the order they were mentioned on
       // the command line.
       //
-      for (here_doc& h: p.second)
+      for (here_doc& h: pr.docs)
       {
         // Switch to the here-line mode which is like single/double-quoted
         // string but recognized the newline as a separator.
@@ -1603,7 +1701,7 @@ namespace build2
         {
           auto i (h.redirects.cbegin ());
 
-          command& c (p.first[i->expr].pipe[i->pipe]);
+          command& c (pr.expr[i->expr].pipe[i->pipe]);
 
           optional<redirect>& r (i->fd == 0 ? c.in  :
                                  i->fd == 1 ? c.out :
@@ -1635,7 +1733,7 @@ namespace build2
           //
           for (++i; i != h.redirects.cend (); ++i)
           {
-            command& c (p.first[i->expr].pipe[i->pipe]);
+            command& c (pr.expr[i->expr].pipe[i->pipe]);
 
             optional<redirect>& ir (i->fd == 0 ? c.in  :
                                     i->fd == 1 ? c.out :
@@ -2062,7 +2160,7 @@ namespace build2
         else if (n == "elif!") r = line_type::cmd_elifn;
         else if (n == "else")  r = line_type::cmd_else;
         else if (n == "while") r = line_type::cmd_while;
-        else if (n == "for")   r = line_type::cmd_for;
+        else if (n == "for")   r = line_type::cmd_for_stream;
         else if (n == "end")   r = line_type::cmd_end;
         else
         {
@@ -2136,10 +2234,11 @@ namespace build2
             {
               line_type lt (j->type);
 
-              if (lt == line_type::cmd_if    ||
-                  lt == line_type::cmd_ifn   ||
-                  lt == line_type::cmd_while ||
-                  lt == line_type::cmd_for)
+              if (lt == line_type::cmd_if         ||
+                  lt == line_type::cmd_ifn        ||
+                  lt == line_type::cmd_while      ||
+                  lt == line_type::cmd_for_stream ||
+                  lt == line_type::cmd_for_args)
                 ++n;
 
               // If we are nested then we just wait until we get back
@@ -2164,10 +2263,8 @@ namespace build2
 
               if (skip)
               {
-                // Note that we don't count else and end as commands.
-                //
-                // @@ Note that for the for-loop's second and third forms
-                //    will probably need to increment li.
+                // Note that we don't count else, end, and 'for x: ...' as
+                // commands.
                 //
                 switch (lt)
                 {
@@ -2176,8 +2273,9 @@ namespace build2
                 case line_type::cmd_ifn:
                 case line_type::cmd_elif:
                 case line_type::cmd_elifn:
-                case line_type::cmd_while: ++li; break;
-                default:                         break;
+                case line_type::cmd_for_stream:
+                case line_type::cmd_while:      ++li; break;
+                default:                              break;
                 }
               }
             }
@@ -2221,7 +2319,10 @@ namespace build2
                   single = true;
               }
 
-              exec_cmd (t, tt, ii, li++, single, ll);
+              exec_cmd (t, tt,
+                        ii, li++, single,
+                        nullptr /* command_function */,
+                        ll);
 
               replay_stop ();
               break;
@@ -2339,7 +2440,147 @@ namespace build2
 
               break;
             }
-          case line_type::cmd_for:
+          case line_type::cmd_for_stream:
+            {
+              // The for-loop construct end. Set on the first iteration.
+              //
+              lines::const_iterator fe (e);
+
+              // Let's "wrap up" all the required data into the single object
+              // to rely on the "small function object" optimization.
+              //
+              struct
+              {
+                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_cond_function>& exec_cond;
+                const function<exec_for_function>& exec_for;
+                const iteration_index* ii;
+                size_t& li;
+                variable_pool* var_pool;
+                decltype (fcend)& fce;
+                lines::const_iterator& fe;
+              } d {i, e,
+                    exec_set, exec_cmd, exec_cond, exec_for,
+                    ii, li,
+                    var_pool,
+                    fcend,
+                    fe};
+
+              function<command_function> cf (
+                [&d, this]
+                (environment& env,
+                 const strings& args,
+                 auto_fd in,
+                 bool pipe,
+                 const optional<deadline>& dl,
+                 const command& deadline_cmd,
+                 const location& ll)
+                {
+                  namespace cli = build2::build::cli;
+
+                  try
+                  {
+                    // Parse arguments.
+                    //
+                    cli::vector_scanner scan (args);
+                    for_options ops (scan);
+
+                    // Note: diagnostics consistent with the set builtin.
+                    //
+                    if (ops.whitespace () && ops.newline ())
+                      fail (ll) << "for: both -n|--newline and "
+                                << "-w|--whitespace specified";
+
+                    if (!scan.more ())
+                      fail (ll) << "for: missing variable name";
+
+                    // Either attributes or variable name.
+                    //
+                    string a (scan.next ());
+                    const string* ats (!scan.more () ? nullptr : &a);
+                    string vname (!scan.more () ? move (a) : scan.next ());
+
+                    if (scan.more ())
+                      fail (ll) << "for: unexpected argument '"
+                                << scan.next () << "'";
+
+                    if (ats != nullptr && ats->empty ())
+                      fail (ll) << "for: empty variable attributes";
+
+                    if (vname.empty ())
+                      fail (ll) << "for: empty variable name";
+
+                    // Let's also diagnose the `... | for x:...` misuse which
+                    // can probably be quite common.
+                    //
+                    if (vname.find (':') != string::npos)
+                      fail (ll) << "for: ':' after variable name";
+
+                    stream_reader sr (
+                      move (in), pipe,
+                      ops.whitespace (), ops.newline (), ops.exact (),
+                      dl, deadline_cmd,
+                      ll);
+
+                    // Since the command pipe is parsed, we can stop
+                    // replaying. Note that we should do this before calling
+                    // exec_lines() for the loop body. Also note that we
+                    // should increment the line index before that.
+                    //
+                    replay_stop ();
+
+                    size_t fli (++d.li);
+                    iteration_index fi {1, d.ii};
+
+                    for (optional<string> s; (s = sr.next ()); )
+                    {
+                      d.li = fli;
+
+                      // Don't move from the variable name since it is used on
+                      // each iteration.
+                      //
+                      env.set_variable (vname,
+                                        names {name (move (*s))},
+                                        ats != nullptr ? *ats : empty_string,
+                                        ll);
+
+                      // Find the construct end, if it is not found yet.
+                      //
+                      if (d.fe == d.e)
+                        d.fe = d.fce (d.i, true, false);
+
+                      if (!exec_lines (d.i + 1, d.fe,
+                                       d.exec_set,
+                                       d.exec_cmd,
+                                       d.exec_cond,
+                                       d.exec_for,
+                                       &fi, d.li,
+                                       d.var_pool))
+                      {
+                        throw exit (true);
+                      }
+
+                      fi.index++;
+                    }
+                  }
+                  catch (const cli::exception& e)
+                  {
+                    fail (ll) << "for: " << e;
+                  }
+                });
+
+              exec_cmd (t, tt, ii, li, false /* single */, cf, ll);
+
+              // Position to construct end.
+              //
+              i = (fe != e ? fe : fcend (i, true, true));
+
+              break;
+            }
+          case line_type::cmd_for_args:
             {
               // Parse the variable name with the potential attributes.
               //
diff --git a/libbuild2/script/parser.hxx b/libbuild2/script/parser.hxx
index 3a4c46f..c402d3e 100644
--- a/libbuild2/script/parser.hxx
+++ b/libbuild2/script/parser.hxx
@@ -97,15 +97,34 @@ namespace build2
       };
       using here_docs = vector<here_doc>;
 
-      pair<command_expr, here_docs>
-      parse_command_expr (token&, token_type&, const redirect_aliases&);
+      struct parse_command_expr_result
+      {
+        command_expr expr; // Single pipe for the for-loop.
+        here_docs    docs;
+        bool         for_loop = false;
+
+        parse_command_expr_result () = default;
+
+        parse_command_expr_result (command_expr&& e,
+                                   here_docs&& h,
+                                   bool f)
+            : expr (move (e)), docs (move (h)), for_loop (f) {}
+      };
+
+      // Pass the first special command program name (token_type::word) if it
+      // is already pre-parsed.
+      //
+      parse_command_expr_result
+      parse_command_expr (token&, token_type&,
+                          const redirect_aliases&,
+                          optional<token>&& program = nullopt);
 
       command_exit
       parse_command_exit (token&, token_type&);
 
       void
       parse_here_documents (token&, token_type&,
-                            pair<command_expr, here_docs>&);
+                            parse_command_expr_result&);
 
       struct parsed_doc
       {
@@ -135,6 +154,11 @@ namespace build2
       // the first two tokens. Use the specified lexer mode to peek the second
       // token.
       //
+      // Always return the cmd_for_stream line type for the for-loop. Note
+      // that the for-loop form cannot be detected easily, based on the first
+      // two tokens. Also note that the detection can be specific for the
+      // script implementation (custom lexing mode, special variables, etc).
+      //
       line_type
       pre_parse_line_start (token&, token_type&, lexer_mode);
 
@@ -169,6 +193,7 @@ namespace build2
       using exec_cmd_function = void (token&, token_type&,
                                       const iteration_index*, size_t li,
                                       bool single,
+                                      const function<command_function>&,
                                       const location&);
 
       using exec_cond_function  = bool (token&, token_type&,
diff --git a/libbuild2/script/run.cxx b/libbuild2/script/run.cxx
index 81abdab..b7f3314 100644
--- a/libbuild2/script/run.cxx
+++ b/libbuild2/script/run.cxx
@@ -9,7 +9,8 @@
 #  include <libbutl/win32-utility.hxx> // DBG_TERMINATE_PROCESS
 #endif
 
-#include <ios> // streamsize
+#include <ios>     // streamsize
+#include <cstring> // strchr()
 
 #include <libbutl/regex.hxx>
 #include <libbutl/builtin.hxx>
@@ -971,81 +972,201 @@ namespace build2
              : path (c.program.recall_string ());
     }
 
-    // Read out the stream content into a string. Throw io_error on the
-    // underlying OS error.
-    //
-    // If the execution deadline is specified, then turn the stream into the
-    // non-blocking mode reading its content in chunks and with a single
-    // operation otherwise. If the specified deadline is reached while
-    // reading the stream, then bail out for the successful deadline and
-    // fail otherwise. Note that in the former case the result will be
-    // incomplete, but we leave it to the caller to handle that.
-    //
-    // Note that on Windows we can only turn pipe file descriptors into the
-    // non-blocking mode. Thus, we have no choice but to read from
-    // descriptors of other types synchronously there. That implies that we
-    // can potentially block indefinitely reading a file and missing the
-    // deadline on Windows. Note though, that the user can normally rewrite
-    // the command, for example, `set foo <<<file` with `cat file | set foo`
-    // to avoid this problem.
-    //
-    static string
-    read (auto_fd in,
+    stream_reader::
+    stream_reader(auto_fd&& in,
 #ifndef _WIN32
-          bool,
+                  bool,
 #else
-          bool pipe,
+                  bool pipe,
 #endif
-          const optional<deadline>& dl,
-          const command& deadline_cmd,
-          const location& ll)
+                  bool ws, bool nl, bool ex,
+                  const optional<deadline>& dl,
+                  const command& dc,
+                  const location& l)
+        : whitespace_ (ws),
+          newline_ (nl),
+          exact_ (ex),
+          deadline_cmd_ (dc),
+          location_ (l)
     {
-      string r;
-      ifdstream cin;
-
 #ifndef _WIN32
       if (dl)
 #else
       if (dl && pipe)
 #endif
       {
-        fdselect_set fds {in.get ()};
-        cin.open (move (in), fdstream_mode::non_blocking);
+        is_.open (move (in), fdstream_mode::non_blocking);
+        deadline_ = dl;
+      }
+      else
+        is_.open (move (in));
+    }
 
-        const timestamp& dlt (dl->value);
+    optional<string> stream_reader::
+    next ()
+    {
+      if (!is_.is_open ())
+        return nullopt;
+
+      // If eos is not reached, then read and return a character. Otherwise
+      // close the stream and return nullopt. If the deadline is specified and
+      // is reached, then return nullopt for the successful deadline (as if
+      // eof is reached) and fail otherwise.
+      //
+      // Set the empty_ flag to false after the first character is read.
+      //
+      auto get = [this] () -> optional<char>
+      {
+        char r;
 
-        for (char buf[4096];; )
+        if (deadline_) // Reading a character in the non-blocking mode.
         {
-          timestamp now (system_clock::now ());
+          fdselect_set fds {is_.fd ()};
 
-          if (dlt <= now || ifdselect (fds, dlt - now) == 0)
+          // Only fallback to ifdselect() if there is no character immediately
+          // available.
+          //
+          for (;;)
           {
-            if (!dl->success)
-              fail (ll) << cmd_path (deadline_cmd)
-                        << " terminated: execution timeout expired";
-            else
+            streamsize n (is_.readsome (&r, 1));
+
+            if (n == 1)
               break;
+
+            if (is_.eof ())
+            {
+              is_.close ();
+              return nullopt;
+            }
+
+            const timestamp& dlt (deadline_->value);
+            timestamp now (system_clock::now ());
+
+            if (dlt <= now || ifdselect (fds, dlt - now) == 0)
+            {
+              is_.close ();
+
+              if (!deadline_->success)
+                fail (location_) << cmd_path (deadline_cmd_)
+                                 << " terminated: execution timeout expired";
+              else
+                return nullopt;
+            }
+          }
+        }
+        else           // Reading a character in the blocking mode.
+        {
+          if (is_.peek () == ifdstream::traits_type::eof ())
+          {
+            is_.close ();
+            return nullopt;
           }
 
-          streamsize n (cin.readsome (buf, sizeof (buf)));
+          is_.get (r);
+        }
 
-          // Bail out if eos is reached.
-          //
-          if (n == 0)
-            break;
+        empty_ = false;
+        return r;
+      };
+
+      if (whitespace_) // The whitespace mode.
+      {
+        const char* sep (" \n\r\t");
+
+        // Note that we collapse multiple consecutive whitespaces.
+        //
+        optional<char> c;
+
+        // Skip the whitespaces.
+        //
+        while ((c = get ()) && strchr (sep, *c) != nullptr) ;
 
-          r.append (buf, n);
+        // Bail out for the trailing whitespace(s) or an empty stream.
+        //
+        if (!c)
+        {
+          // Return the trailing "blank" after the trailing whitespaces in the
+          // exact mode, unless the stream is empty.
+          //
+          return exact_ && !empty_ ? empty_string : optional<string> ();
         }
+
+        // Read the word until eof or a whitespace character is encountered.
+        //
+        string r (1, *c);
+        while ((c = get ()) && strchr (sep, *c) == nullptr)
+          r += *c;
+
+        return optional<string> (move (r));
       }
-      else
+      else             // The newline or no-split mode.
       {
-        cin.open (move (in));
-        r = cin.read_text ();
-      }
+        // Note that we don't collapse multiple consecutive newlines.
+        //
+        // Note also that we always sanitize CRs, so in the no-split mode we
+        // need to loop rather than read the whole text at once.
+        //
+        optional<string> r;
 
-      cin.close ();
+        do
+        {
+          string l;
+          optional<char> c;
 
-      return r;
+          // Read the line until eof or newline character is encountered.
+          //
+          while ((c = get ()) && *c != '\n')
+            l += *c;
+
+          // Strip the trailing CRs that can appear while, for example,
+          // cross-testing Windows target or as a part of msvcrt junk
+          // production (see above).
+          //
+          while (!l.empty () && l.back () == '\r')
+            l.pop_back ();
+
+          // Append the line.
+          //
+          if (!l.empty () || // Non-empty.
+              c           || // Empty, non-trailing.
+              (exact_ &&     // Empty, trailing, in the exact mode for
+               !empty_))     // non-empty stream.
+          {
+            if (newline_ || !r)
+            {
+              r = move (l);
+            }
+            else
+            {
+              *r += '\n';
+              *r += l;
+            }
+          }
+        }
+        while (!newline_ && is_.is_open ());
+
+        return r;
+      }
+    }
+
+    string
+    stream_read (auto_fd&& in,
+                 bool pipe,
+                 const optional<deadline>& dl,
+                 const command& dc,
+                 const location& ll)
+    {
+      stream_reader sr (move (in),
+                        pipe,
+                        false /* whitespace */,
+                        false /* newline */,
+                        true /* exact */,
+                        dl,
+                        dc,
+                        ll);
+
+      optional<string> s (sr.next ());
+      return s ? move (*s) : empty_string;
     }
 
     // The set pseudo-builtin: set variable from the stdin input.
@@ -1087,87 +1208,17 @@ namespace build2
         if (vname.empty ())
           fail (ll) << "set: empty variable name";
 
-        // Read out the stream content into a string while keeping an eye on
-        // the deadline.
-        //
-        string s (read (move (in), pipe, dl, deadline_cmd, ll));
+        stream_reader sr (move (in), pipe,
+                          ops.whitespace (), ops.newline (), ops.exact (),
+                          dl, deadline_cmd,
+                          ll);
 
         // Parse the stream content into the variable value.
         //
         names ns;
 
-        if (!s.empty ())
-        {
-          if (ops.whitespace ()) // The whitespace mode.
-          {
-            // Note that we collapse multiple consecutive whitespaces.
-            //
-            for (size_t p (0); p != string::npos; )
-            {
-              // Skip the whitespaces.
-              //
-              const char* sep (" \n\r\t");
-              size_t b (s.find_first_not_of (sep, p));
-
-              if (b != string::npos) // Word beginning.
-              {
-                size_t e (s.find_first_of (sep, b)); // Find the word end.
-                ns.emplace_back (string (s, b, e != string::npos ? e - b : e));
-
-                p = e;
-              }
-              else // Trailings whitespaces.
-              {
-                // Append the trailing "blank" after the trailing whitespaces
-                // in the exact mode.
-                //
-                if (ops.exact ())
-                  ns.emplace_back (empty_string);
-
-                // Bail out since the end of the string is reached.
-                //
-                break;
-              }
-            }
-          }
-          else // The newline or no-split mode.
-          {
-            // Note that we don't collapse multiple consecutive newlines.
-            //
-            // Note also that we always sanitize CRs so this loop is always
-            // needed.
-            //
-            for (size_t p (0); p != string::npos; )
-            {
-              size_t e (s.find ('\n', p));
-              string l (s, p, e != string::npos ? e - p : e);
-
-              // Strip the trailing CRs that can appear while, for example,
-              // cross-testing Windows target or as a part of msvcrt junk
-              // production (see above).
-              //
-              while (!l.empty () && l.back () == '\r')
-                l.pop_back ();
-
-              // Append the line.
-              //
-              if (!l.empty ()       || // Non-empty.
-                  e != string::npos || // Empty, non-trailing.
-                  ops.exact ())        // Empty, trailing, in the exact mode.
-              {
-                if (ops.newline () || ns.empty ())
-                  ns.emplace_back (move (l));
-                else
-                {
-                  ns[0].value += '\n';
-                  ns[0].value += l;
-                }
-              }
-
-              p = e != string::npos ? e + 1 : e;
-            }
-          }
-        }
+        for (optional<string> s; (s = sr.next ()); )
+          ns.emplace_back (move (*s));
 
         env.set_variable (move (vname),
                           move (ns),
@@ -1242,7 +1293,7 @@ namespace build2
               const iteration_index* ii, size_t li, size_t ci,
               const location& ll,
               bool diag,
-              string* output,
+              const function<command_function>& cf, bool last_cmd,
               optional<deadline> dl = nullopt,
               const command* dl_cmd = nullptr, // env -t <cmd>
               pipe_command* prev_cmd = nullptr)
@@ -1253,8 +1304,10 @@ namespace build2
       //
       if (bc == ec)
       {
-        if (output != nullptr)
+        if (cf != nullptr)
         {
+          assert (!last_cmd); // Otherwise we wouldn't be here.
+
           // The pipeline can't be empty.
           //
           assert (ifd != nullfd && prev_cmd != nullptr);
@@ -1263,15 +1316,14 @@ namespace build2
 
           try
           {
-            *output = read (move (ifd),
-                            true /* pipe */,
-                            dl,
-                            dl_cmd != nullptr ? *dl_cmd : c,
-                            ll);
+            cf (env, strings () /* arguments */,
+                move (ifd), true /* pipe */,
+                dl, dl_cmd != nullptr ? *dl_cmd : c,
+                ll);
           }
           catch (const io_error& e)
           {
-            fail (ll) << "io error reading " << cmd_path (c) << " output: "
+            fail (ll) << "unable to read from " << cmd_path (c) << " output: "
                       << e;
           }
         }
@@ -1329,9 +1381,10 @@ namespace build2
       command_pipe::const_iterator nc (bc + 1);
       bool last (nc == ec);
 
-      // Make sure that stdout is not redirected if meant to be read.
+      // Make sure that stdout is not redirected if meant to be read (last_cmd
+      // is false) or cannot not be produced (last_cmd is true).
       //
-      if (last && output != nullptr && c.out)
+      if (last && c.out && cf != nullptr)
         fail (ll) << "stdout cannot be redirected";
 
       // True if the process path is not pre-searched and the program path
@@ -1345,7 +1398,7 @@ namespace build2
 
       const redirect& in ((c.in ? *c.in : env.in).effective ());
 
-      const redirect* out (!last || output != nullptr
+      const redirect* out (!last || (cf != nullptr && !last_cmd)
                            ? nullptr // stdout is piped.
                            : &(c.out ? *c.out : env.out).effective ());
 
@@ -1413,7 +1466,7 @@ namespace build2
         if (c.out)
           fail (ll) << program << " builtin stdout cannot be redirected";
 
-        if (output != nullptr)
+        if (cf != nullptr && !last_cmd)
           fail (ll) << program << " builtin stdout cannot be read";
 
         if (c.err)
@@ -1620,7 +1673,7 @@ namespace build2
         if (c.out)
           fail (ll) << "set builtin stdout cannot be redirected";
 
-        if (output != nullptr)
+        if (cf != nullptr && !last_cmd)
           fail (ll) << "set builtin stdout cannot be read";
 
         if (c.err)
@@ -1640,6 +1693,39 @@ namespace build2
         return true;
       }
 
+      // If this is the last command in the pipe and the command function is
+      // specified for it, then call it.
+      //
+      if (last && cf != nullptr && last_cmd)
+      {
+        // Must be enforced by the caller.
+        //
+        assert (!c.out && !c.err && !c.exit);
+
+        try
+        {
+          cf (env, c.arguments,
+              move (ifd), !first,
+              dl, dl_cmd != nullptr ? *dl_cmd : c,
+              ll);
+        }
+        catch (const io_error& e)
+        {
+          diag_record dr (fail (ll));
+
+          dr << cmd_path (c) << ": unable to read from ";
+
+          if (prev_cmd != nullptr)
+            dr << cmd_path (prev_cmd->cmd) << " output";
+          else
+            dr << "stdin";
+
+          dr << ": " << e;
+        }
+
+        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
@@ -2220,7 +2306,7 @@ namespace build2
                               nc, ec,
                               move (ofd.in),
                               ii, li, ci + 1, ll, diag,
-                              output,
+                              cf, last_cmd,
                               dl, dl_cmd,
                               &pc);
 
@@ -2347,7 +2433,7 @@ namespace build2
                               nc, ec,
                               move (ofd.in),
                               ii, li, ci + 1, ll, diag,
-                              output,
+                              cf, last_cmd,
                               dl, dl_cmd,
                               &pc);
 
@@ -2487,7 +2573,7 @@ namespace build2
               const iteration_index* ii, size_t li,
               const location& ll,
               bool diag,
-              string* output)
+              const function<command_function>& cf, bool last_cmd)
     {
       // Commands are numbered sequentially throughout the expression
       // starting with 1. Number 0 means the command is a single one.
@@ -2532,7 +2618,7 @@ namespace build2
                         p.begin (), p.end (),
                         auto_fd (),
                         ii, li, ci, ll, print,
-                        output);
+                        cf, last_cmd);
         }
 
         ci += p.size ();
@@ -2546,13 +2632,18 @@ namespace build2
          const command_expr& expr,
          const iteration_index* ii, size_t li,
          const location& ll,
-         string* output)
+         const function<command_function>& cf,
+         bool last_cmd)
     {
       // 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, ii, li, ll, true /* diag */, output))
+      if (!run_expr (env,
+                     expr,
+                     ii, li, ll,
+                     true /* diag */,
+                     cf, last_cmd))
         throw failed (); // Assume diagnostics is already printed.
     }
 
@@ -2561,11 +2652,15 @@ namespace build2
               const command_expr& expr,
               const iteration_index* ii, size_t li,
               const location& ll,
-              string* output)
+              const function<command_function>& cf, bool last_cmd)
     {
       // Note that we don't print the expression here (see above).
       //
-      return run_expr (env, expr, ii, li, ll, false /* diag */, output);
+      return run_expr (env,
+                       expr,
+                       ii, li, ll,
+                       false /* diag */,
+                       cf, last_cmd);
     }
 
     void
diff --git a/libbuild2/script/run.hxx b/libbuild2/script/run.hxx
index 01b010c..5d46d21 100644
--- a/libbuild2/script/run.hxx
+++ b/libbuild2/script/run.hxx
@@ -38,22 +38,24 @@ namespace build2
     // Location is the start position of this command line in the script. It
     // can be used in diagnostics.
     //
-    // Optionally, save the command output into the referenced variable. In
-    // this case assume that the expression contains a single pipline.
+    // Optionally, execute the specified function at the end of the pipe,
+    // either after the last command or instead of it.
     //
     void
     run (environment&,
          const command_expr&,
          const iteration_index*, size_t index,
          const location&,
-         string* output = nullptr);
+         const function<command_function>& = nullptr,
+         bool last_cmd = true);
 
     bool
     run_cond (environment&,
               const command_expr&,
               const iteration_index*, size_t index,
               const location&,
-              string* output = nullptr);
+              const function<command_function>& = nullptr,
+              bool last_cmd = true);
 
     // Perform the registered special file cleanups in the direct order and
     // then the regular cleanups in the reverse order.
@@ -80,6 +82,62 @@ namespace build2
     //
     string
     diag_path (const dir_name_view&);
+
+    // Read out the stream content into a string, optionally splitting the
+    // input data at whitespaces or newlines in which case return one
+    // sub-string at a time (see the set builtin options for the splitting
+    // semantics). Throw io_error on the underlying OS error.
+    //
+    // If the execution deadline is specified, then turn the stream into the
+    // non-blocking mode. If the specified deadline is reached while reading
+    // the stream, then bail out for the successful deadline and fail
+    // otherwise. Note that in the former case the result will be incomplete,
+    // but we leave it to the caller to handle that.
+    //
+    // Note that on Windows we can only turn pipe file descriptors into the
+    // non-blocking mode. Thus, we have no choice but to read from descriptors
+    // of other types synchronously there. That implies that we can
+    // potentially block indefinitely reading a file and missing the deadline
+    // on Windows. Note though, that the user can normally rewrite the
+    // command, for example, `set foo <<<file` with `cat file | set foo` to
+    // avoid this problem.
+    //
+    class stream_reader
+    {
+    public:
+      stream_reader (auto_fd&&,
+                     bool pipe,
+                     bool whitespace, bool newline, bool exact,
+                     const optional<deadline>&,
+                     const command& deadline_cmd,
+                     const location&);
+
+      // Return nullopt if eos is reached.
+      //
+      optional<string>
+      next ();
+
+    private:
+      ifdstream is_;
+      bool whitespace_;
+      bool newline_;
+      bool exact_;
+      optional<deadline> deadline_;
+      const command& deadline_cmd_;
+      const location& location_;
+
+      bool empty_ = true; // Set to false after the first character is read.
+    };
+
+    // Read the stream content using the stream reader in the no-split exact
+    // mode.
+    //
+    string
+    stream_read (auto_fd&&,
+                 bool pipe,
+                 const optional<deadline>&,
+                 const command& deadline_cmd,
+                 const location&);
   }
 }
 
diff --git a/libbuild2/script/script.cxx b/libbuild2/script/script.cxx
index 33c4c30..b8dfc68 100644
--- a/libbuild2/script/script.cxx
+++ b/libbuild2/script/script.cxx
@@ -20,16 +20,17 @@ namespace build2
 
       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_while: s = "'while'";  break;
-      case line_type::cmd_for:   s = "'for'";    break;
-      case line_type::cmd_end:   s = "'end'";    break;
+      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_while:      s = "'while'";  break;
+      case line_type::cmd_for_args:   s = "'for'";    break;
+      case line_type::cmd_for_stream: s = "'for'";    break;
+      case line_type::cmd_end:        s = "'end'";    break;
       }
 
       return o << s;
@@ -227,7 +228,8 @@ namespace build2
         case line_type::cmd_elifn:
         case line_type::cmd_else:
         case line_type::cmd_while:
-        case line_type::cmd_for:   fc_ind += "  "; break;
+        case line_type::cmd_for_args:
+        case line_type::cmd_for_stream: fc_ind += "  "; break;
         default: break;
         }
 
diff --git a/libbuild2/script/script.hxx b/libbuild2/script/script.hxx
index 5eb4ee9..aa96b7f 100644
--- a/libbuild2/script/script.hxx
+++ b/libbuild2/script/script.hxx
@@ -28,7 +28,8 @@ namespace build2
       cmd_elifn,
       cmd_else,
       cmd_while,
-      cmd_for,
+      cmd_for_args,   // `for x: ...`
+      cmd_for_stream, // `... | for x` and `for x <...`
       cmd_end
     };
 
@@ -42,7 +43,7 @@ namespace build2
 
       union
       {
-        const variable* var; // Pre-entered for line_type::var.
+        const variable* var; // Pre-entered for line_type::{var,cmd_for_*}.
       };
     };
 
@@ -547,7 +548,7 @@ namespace build2
       // Set variable value with optional (non-empty) attributes.
       //
       virtual void
-      set_variable (string&& name,
+      set_variable (string name,
                     names&&,
                     const string& attrs,
                     const location&) = 0;
@@ -580,6 +581,17 @@ namespace build2
       ~environment () = default;
     };
 
+    // Custom command function that can be executed at the end of the pipe.
+    // Should throw io_error on the underlying OS error.
+    //
+    using command_function = void (environment&,
+                                   const strings& args,
+                                   auto_fd in,
+                                   bool pipe,
+                                   const optional<deadline>&,
+                                   const command& deadline_cmd,
+                                   const location&);
+
     // Helpers.
     //
     // Issue diagnostics with the specified prefix and fail if the string