On 13/06/2014 03:11, Nikolaus Rath wrote:
> "R. David Murray" <rdmur...@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
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