[Patches] [ python-Patches-466451 ] popen fix for multiple quoted arguments

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Patches item #466451, was opened at 2001-09-29 17:34
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Category: Core (C code)
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Brian Quinlan (bquinlan)
>Assigned to: Mark Hammond (mhammond)
Summary: popen fix for multiple quoted arguments

Initial Comment:
In a Windows version of Python, try the following:

os.popen('"<path-of-exe" "path-of-arg"'>.read()

cmd.exe will misinterpret the command string because 
it strips the first and last quote in the command 
string (cmd.exe /? for details).

This patch does a few things:

1. it encloses the command string sent to cmd.exe in 
quotes and uses the /S switch

2. if the shell is not command.com or cmd.exe, it 
passes the -c switch to the shell (this makes popen 
work if the user's shell is bash, sh, etc.)

3. changes the variables s1, s2 and s3 to cmdPath, 
completeCmd and cmdArgs

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>Comment By: Tim Peters (tim_one)
Date: 2001-10-01 15:36

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Assigned to MarkH for further pondering.

I like giving vrbls useful names  The rest seems highly 
dubious:

+ Catering to non-MS shells ("-c" vs "/C") is a fine idea, 
but what about 4DOS or 4NT, or other non-MS shells that 
also expect /C?  It looks like this patch will kill people 
using them.

- It's not backwards compatible regardless of shell (as 
Brian pointed out).

- It's surprising to anyone who has read the cmd docs and 
expects cmd.exe to work as documented (by MS).

- Since it's unique to Python's popen, a command string 
that works for popen() may break if passed to os.system() 
instead, and vice versa, and maybe for os.startfile() too.

Other things bug me, but I'll stop there <wink>.  The MS 
shells are a godawful mess, and it would really be nice to 
supply a rational x-platform "virtual shell" syntax (as Tcl 
does for its "exec" cmd).  Short of that, I'm not sure a 
collection of inconsistent and undocumented hacks is 
actually progress; as is, Python's behavior is at least 
predictable from reading the MS docs and/or playing with C 
programs under MSVC.

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Comment By: Brian Quinlan (bquinlan)
Date: 2001-09-30 13:11

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Mark understands the issue; I've already talked to him 
about this. 

Another thing that I should have noted is that this patch 
does NOT ensure backwards compatibility. Any scripts that 
manually quote their command strings, to work around this 
problem, will break.

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Comment By: Guido van Rossum (gvanrossum)
Date: 2001-09-30 11:46

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Tim, whaddayathink? Or is this for Mark?

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