From 3fa1b103014bab51f8f257e1e12f27f7e498f42e Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Fri, 13 Sep 2019 20:57:00 +0300
Subject: Add support for builtin escaping to command running API

---
 libbutl/command.cxx      | 12 +++++++++++-
 libbutl/command.mxx      |  5 +++++
 tests/command/testscript | 10 ++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/libbutl/command.cxx b/libbutl/command.cxx
index a344790..1126bb0 100644
--- a/libbutl/command.cxx
+++ b/libbutl/command.cxx
@@ -272,11 +272,21 @@ namespace butl
     }
     else               // Execute the program.
     {
+      // Strip the potential leading `^`, indicating that this is an external
+      // program rather than a builtin. Consider only simple paths and don't
+      // end up with an empty path.
+      //
+      const char* p (prog.size () > 1 &&
+                     prog[0] == '^'   &&
+                     path::traits_type::find_separator (prog) == string::npos
+                     ? prog.c_str () + 1
+                     : prog.c_str ());
+
       // Prepare the process environment.
       //
       // Note: cwd passed to process_env() may not be a temporary object.
       //
-      process_env pe (prog, cwd, env ? env->vars : nullptr);
+      process_env pe (p, cwd, env ? env->vars : nullptr);
 
       // Finally, run the process.
       //
diff --git a/libbutl/command.mxx b/libbutl/command.mxx
index 0e6617b..8423f59 100644
--- a/libbutl/command.mxx
+++ b/libbutl/command.mxx
@@ -37,6 +37,11 @@ LIBBUTL_MODEXPORT namespace butl
   // error, ios::failure on the underlying OS error, process_error on the
   // process running error and std::system_error on the builtin running error.
   //
+  // To run a system utility rather than a builtin prefix its name with `^`,
+  // for example:
+  //
+  // ^cat --squeeze-blank file
+  //
   // The process environment path is unused and must point to the empty
   // process path.
   //
diff --git a/tests/command/testscript b/tests/command/testscript
index db9bb5c..12ddd79 100644
--- a/tests/command/testscript
+++ b/tests/command/testscript
@@ -184,4 +184,14 @@ end
   {
     $* -p 'echo abc >a' >'echo abc >a' &a
   }
+
+  : escape
+  :
+  : Note that the sed builtin doesn't support multiple scripts.
+  :
+  if ($cxx.target.class != 'windows')
+  {
+    echo 'abc' >=f;
+    $* '^sed -e s/a/b/ -e s/c/b/ f' >'bbb'
+  }
 }
-- 
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