New submission from Dave Abrahams <d...@boostpro.com>:
On POSIX systems, the PATH environment variable is always used to
look up directory-less executable names passed as the first argument to
Popen(...), but on Windows, PATH is only considered when shell=True is also
passed.
Actually I think it may be slightly weirder than that when
shell=False, because the following holds for me:
C:\>rem ##### Prepare minimal PATH #####
C:\>set
"PATH=C:\Python26\Scripts;C:\Python26;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem"
C:\>rem ##### Prepare a minimal, clean environment #####
C:\>virtualenv --no-site-packages e:\zzz
New python executable in e:\zzz\Scripts\python.exe
Installing setuptools................done.
C:\>rem ##### Show that shell=True makes the difference in determining whether
PATH is respected #####
C:\>python
Python 2.6.5 (r265:79096, Mar 19 2010, 18:02:59) [MSC v.1500 64 bit (AMD64)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import subprocess
>>> subprocess.Popen(['python', '-c', 'import sys; print sys.executable'])
<subprocess.Popen object at 0x0000000001DBE080>
>>> C:\Python26\python.exe
>>> subprocess.Popen(['python', '-c', 'import sys; print sys.executable'],
>>> env={'PATH':r'e:\zzz\Scripts'})
<subprocess.Popen object at 0x0000000001F05A90>
>>> C:\Python26\python.exe
>>> subprocess.Popen(['python', '-c', 'import sys; print sys.executable'],
>>> env={'PATH':r'e:\zzz\Scripts'}, shell=True)
<subprocess.Popen object at 0x0000000001F05B00>
>>> e:\zzz\Scripts\python.exe
That is, it looks like the environment at the time Python is invoked is what
counts unless I pass shell=True. I don't even seem to be able to override this
behavior by changing os.environ: you can clear() it and pass env={} and
subprocess.Popen(['python']) still succeeds.
This is a very important problem for portable code and one that took me hours
to suss out. I think:
a) the current behavior needs to be documented
b) it needs to be fixed if possible
c) otherwise, shell=True should be the default
----------
assignee: d...@python
components: Documentation
messages: 104422
nosy: dabrahams, d...@python
priority: normal
severity: normal
status: open
title: subprocess portability issue
type: behavior
versions: Python 2.6
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue8557>
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