escaping characters in filenames

Nobody nobody at nowhere.com
Wed Jul 29 20:55:16 CEST 2009


On Wed, 29 Jul 2009 09:29:55 -0400, J Kenneth King wrote:

> I wrote a script to process some files using another program.  One thing
> I noticed was that both os.listdir() and os.path.walk() will return
> unescaped file names (ie: "My File With Spaces & Stuff" instead of "My\
> File\ With\ Spaces\ \&\ Stuff").  I haven't had much success finding a
> module or recipe that escapes file names and was wondering if anyone
> could point me in the right direction.
> 
> As an aside, the script is using subprocess.call() with the "shell=True"
> parameter.  There isn't really a reason for doing it this way (was just
> the fastest way to write it and get a prototype working).  I was
> wondering if Popen objects were sensitive to unescaped names like the
> shell.  I intend to refactor the function to use Popen objects at some
> point and thought perhaps escaping file names may not be entirely
> necessary.

Note that subprocess.call() is nothing more than:

	def call(*popenargs, **kwargs):
	    return Popen(*popenargs, **kwargs).wait()

plus a docstring. It accepts exactly the same arguments as Popen(), with
the same semantics.

If you want to run a command given a program and arguments, you
should pass the command and arguments as a list, rather than trying to
construct a string.

On Windows the value of shell= is unrelated to whether the command is
a list or a string; a list is always converted to string using the
list2cmdline() function. Using shell=True simply prepends "cmd.exe /c " to
the string (this allows you to omit the .exe/.bat/etc extension for
extensions which are in %PATHEXT%).

On Unix, a string is first converted to a single-element list, so if you
use a string with shell=False, it will be treated as the name of an
executable to be run without arguments, even if contains spaces, shell
metacharacters etc.

The most portable approach seems to be to always pass the command as a
list, and to set shell=True on Windows and shell=False on Unix.

The only reason to pass a command as a string is if you're getting a
string from the user and you want it to be interpreted using the
platform's standard shell (i.e. cmd.exe or /bin/sh). If you want it to be
interpreted the same way regardless of platform, parse it into a
list using shlex.split().




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