Use PATH from env argument to pexpect.spawn

Currently pexpect.spawn takes an env argument along the lines of
subprocess.Popen but fails to use PATH from that env when finding
the binary to run.

The result when running a binary not on the PATH of the parent
process is pexpect will raise an exception, or worse, find a
different binary with the same name.

This change passes the env from spawn into the which function
so the correct PATH is searched and adds test coverage.

2 files changed, 6 insertions, 5 deletions

diff --git a/pexpect/pty_spawn.py b/pexpect/pty_spawn.py
index 3518cc1..e5b5814 100644
--- a/pexpect/pty_spawn.py
+++ b/pexpect/pty_spawn.py
@@ -266,7 +266,7 @@ class spawn(SpawnBase):
             self.args.insert(0, command)
             self.command = command
 
-        command_with_path = which(self.command)
+        command_with_path = which(self.command, env=self.env)
         if command_with_path is None:
             raise ExceptionPexpect('The command was not found or was not ' +
                     'executable: %s.' % self.command)
diff --git a/pexpect/utils.py b/pexpect/utils.py
index 737f0ed..c2763c4 100644
--- a/pexpect/utils.py
+++ b/pexpect/utils.py
@@ -31,7 +31,7 @@ def is_executable_file(path):
     return os.access(fpath, os.X_OK)
 
 
-def which(filename):
+def which(filename, env=None):
     '''This takes a given filename; tries to find it in the environment path;
     then checks if it is executable. This returns the full path to the filename
     if found and executable. Otherwise this returns None.'''
@@ -39,10 +39,11 @@ def which(filename):
     # Special case where filename contains an explicit path.
     if os.path.dirname(filename) != '' and is_executable_file(filename):
         return filename
-    if 'PATH' not in os.environ or os.environ['PATH'] == '':
+    if env is None:
+        env = os.environ
+    p = env.get('PATH')
+    if not p:
         p = os.defpath
-    else:
-        p = os.environ['PATH']
     pathlist = p.split(os.pathsep)
     for path in pathlist:
         ff = os.path.join(path, filename)