From 8299ce49ea3ded1ae83104fa182a8a608cd83ae0 Mon Sep 17 00:00:00 2001
From: adam j hartz <hartz@mit.edu>
Date: Sat, 19 Dec 2015 17:59:41 -0500
Subject: [PATCH] modify expandvars to use the xonsh environment

---
 xonsh/built_ins.py |  4 ++--
 xonsh/tools.py     | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/xonsh/built_ins.py b/xonsh/built_ins.py
index d19efec18..a53b6503c 100644
--- a/xonsh/built_ins.py
+++ b/xonsh/built_ins.py
@@ -22,7 +22,7 @@ from collections import Sequence, MutableMapping, Iterable, namedtuple, \
     MutableSequence, MutableSet
 
 from xonsh.tools import suggest_commands, XonshError, ON_POSIX, ON_WINDOWS, \
-    string_types
+    string_types, expandvars
 from xonsh.inspectors import Inspector
 from xonsh.environ import Env, default_env, locate_binary
 from xonsh.aliases import DEFAULT_ALIASES
@@ -183,7 +183,7 @@ def expand_path(s):
     if ENV is not None:
         ENV.replace_env()
     if ENV.get('EXPAND_ENV_VARS'):
-        s = os.path.expandvars(s)
+        s = expandvars(s)
     return os.path.expanduser(s)
 
 
diff --git a/xonsh/tools.py b/xonsh/tools.py
index 4f6b4b57d..ccd07f416 100644
--- a/xonsh/tools.py
+++ b/xonsh/tools.py
@@ -909,3 +909,46 @@ def check_for_partial_string(x):
         return (string_indices[-1], None, starting_quote[-1])
     else:
         return (string_indices[-2], string_indices[-1], starting_quote[-1])
+
+
+# expandvars is a modified version of os.path.expandvars from the Python 3.5.1
+# source code (root/Lib/posixpath.py, line 266)
+
+_varprog = None
+
+
+def expandvars(path):
+    """Expand shell variables of form $var and ${var}.  Unknown variables
+    are left unchanged."""
+    global _varprog
+    ENV = builtins.__xonsh_env__
+    if isinstance(path, bytes):
+        path = path.decode(encoding=env.get('XONSH_ENCODING'),
+                           errors=env.get('XONSH_ENCODING_ERRORS'))
+    if '$' not in path:
+        return path
+    if not _varprog:
+        import re
+        _varprog = re.compile(r'\$(\w+|\{[^}]*\})', re.ASCII)
+    search = _varprog.search
+    start = '{'
+    end = '}'
+    i = 0
+    while True:
+        m = search(path, i)
+        if not m:
+            break
+        i, j = m.span(0)
+        name = m.group(1)
+        if name.startswith(start) and name.endswith(end):
+            name = eval(name[1:-1]) # change for non-POSIX ${...}
+        try:
+            value = ENV.get(name)
+        except KeyError:
+            i = j
+        else:
+            tail = path[j:]
+            path = path[:i] + value
+            i = len(path)
+            path += tail
+    return path