[Python-Dev] subprocess shell=True on Windows doesn't escape ^ character

[Tim Golden]

On 13/06/2014 03:11, Nikolaus Rath wrote:
> "R. David Murray" <rdmurray at bitdance.com> writes:
>> Also notice that using a list with shell=True is using the API
>> incorrectly.  It wouldn't even work on Linux, so that torpedoes
>> the cross-platform concern already :)
>>
>> This kind of confusion is why I opened http://bugs.python.org/issue7839.
> 
> Can someone describe an use case where shell=True actually makes sense
> at all?

On Windows (where I think the OP is), Popen & friends ultimately invoke
CreateProcess.

In the case where shell=True, subprocess invokes the command interpreter
explictly under the covers and tweaks a few other things to avoid a
Brief Flash of Unstyled Console. This is the relevant snippet from
subprocess.py:

            if shell:
                startupinfo.dwFlags |= _winapi.STARTF_USESHOWWINDOW
                startupinfo.wShowWindow = _winapi.SW_HIDE
                comspec = os.environ.get("COMSPEC", "cmd.exe")
                args = '{} /c "{}"'.format (comspec, args)


That's all. It's more or less equivalent to your prefixing your commands
with "cmd.exe /c".

The only reasons you should need to do this are:

* If you're using one of the few commands which are actually built-in to
cmd.exe. I can't quickly find an online source for these, but typical
examples will be: "dir" or "copy".

* In some situations -- and I've never been able to nail this -- if
you're trying to run a .bat/.cmd file. I've certainly been able to run
batch files without shell=True but other people have failed within what
appears to  be the same configuration unless invoking cmd.exe via
shell=True.

I use hg.exe (from TortoiseHg) but ISTR that the base Mercurial install
supplies a .bat/.cmd. If that's the OP's case then he might find it
necessary to pass shell=True.


TJG