[stdlib-sig] quoting arguments for command-line evaluation

[C. Titus Brown]

On Mon, May 24, 2010 at 07:46:32AM -0700, Bill Janssen wrote:
> I'm kind of surprised to see that the subprocess module doesn't have a
> documented function for calling to properly quote command-line
> arguments.  Nor does it seem to do so automatically -- at least on Unix.

Bill, I may be about to reveal my profound ignorance here, but...

do you need to quote arguments passed as a list on UNIX?  My impression
was that if shell=False, then it wasn't needed.

> It *does* have an undocumented function called "list2cmdline" (refered
> to in passing in the docs as a "method"), which is called automatically
> if the "args" parameter to the Popen() initializer is a sequence, and
> the platform is Windows, but not otherwise.  No similar quoting of args
> is done for Unix.
> 
> On the other hand, the "pipes" module has another undocumented function
> called "quote", which seems to perform similar quoting, but for sh.
> "Pipes" is documented to work only under Unix -- which is a bit strange,
> as cmd.exe supports pipes on Windows as well.
> 
> Given that Python, even 3, ships with os.system() and os.popen() and
> subprocess and pipes and perhaps others that I don't know about,
> exposing a quoting mechanism that appropriately quotes for either sh or
> cmd.exe, depending on platform, wouldn't be a bad idea.  And perhaps
> pipes should be eliminated, or re-written in terms of subprocess to be
> cross-platform.

Yeah, this whole part of the stdlib is a small horror show.

(I didn't even know the 'pipes' module existed... wow.)

--titus
-- 
C. Titus Brown, ctb at msu.edu