subprocess and & (ampersand)

[Steven D'Aprano]

On Tue, 22 Jan 2008 22:53:20 -0700, Steven Bethard wrote:

> I'm having trouble using the subprocess module on Windows when my
> command line includes special characters like "&" (ampersand)::
> 
>  >>> command = 'lynx.bat', '-dump', 'http://www.example.com/?x=1&y=2'
>  >>> kwargs = dict(stdin=subprocess.PIPE,
> ...               stdout=subprocess.PIPE, ...              
> stderr=subprocess.PIPE)
>  >>> proc = subprocess.Popen(command, **kwargs) proc.stderr.read()
> "'y' is not recognized as an internal or external command,\r\noperable
> program or batch file.\r\n"
> 
> As you can see, Windows is interpreting that "&" as separating two
> commands, instead of being part of the single argument as I intend it to
> be above.  Is there any workaround for this?  How do I get "&" treated
> like a regular character using the subprocess module?


That's nothing to do with the subprocess module. As you say, it is 
Windows interpreting the ampersand as a special character, so you need to 
escape the character to the Windows shell.

Under Windows, the escape character is ^, or you can put the string in 
double quotes:

# untested
command = 'lynx.bat -dump http://www.example.com/?x=1^&y=2'
command = 'lynx.bat -dump "http://www.example.com/?x=1&y=2"'

In Linux land, you would use a backslash or quotes.

To find the answer to this question, I googled for "windows how to escape 
special characters shell" and found these two pages:


http://www.microsoft.com/technet/archive/winntas/deploy/prodspecs/shellscr.mspx

http://technet2.microsoft.com/WindowsServer/en/library/44500063-fdaf-4e4f-8dac-476c497a166f1033.mspx


Hope this helps,



-- 
Steven