Fix prompt exporting escaped characters, opt into PS1 mod.

go/env.py

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Can be used to point environment variable to hermetic Go toolset.
 
 Usage (on linux and mac):
 $ eval `./env.py`
 $ go version
@@ skipping 11 matching lines @@
 import subprocess
 import sys
 
 # Do not want to mess with sys.path, load the module directly.
 bootstrap = imp.load_source(
     'bootstrap', os.path.join(os.path.dirname(__file__), 'bootstrap.py'))
 
 old = os.environ.copy()
 new = bootstrap.prepare_go_environ()
 
+def _escape_special(v):
+  """Returns (str): The supplied value, with special shell characters escaped.
+
+  Replace special characters with their escaped form. This will allow them
+  to be interpreted by the shell using the $'...' notation.
+
+  Args:
+    v (str): The input value to escape.
+  """
+  for f, r in (
+      ('\n', '\\n'),
+      ('\b', '\\b'),
+      ('\r', '\\r'),
+      ('\t', '\\t'),
+      ('\v', '\\v')):
+    v = v.replace(f, r)
+  return v
+
 if len(sys.argv) == 1:
   for key, value in sorted(new.iteritems()):
     if old.get(key) != value:
-      print 'export %s=%s' % (key, pipes.quote(value))
+      orig_value, value = value, _escape_special(value)
+
+      # We will only use the $'...' notation if there was an escaped character
+      # in the string.
+      print 'export %s=%s%s' % (key, ('$') if orig_value != value else (''),
+                                pipes.quote(value))
 else:
   exe = sys.argv[1]
   if exe == 'python':
     exe = sys.executable
   else:
     # Help Windows to find the executable in new PATH, do it only when
     # executable is referenced by name (and not by path).
     if os.sep not in exe:
       exe = bootstrap.find_executable(exe, [bootstrap.WORKSPACE])
   sys.exit(subprocess.call([exe] + sys.argv[2:], env=new))