Python subprocess module, how do I give input to the first of series of piped commands?

Question

I am trying to use Python\'s subprocess module. What I require is to send input to the first process whose output becomes the input of the second process. The situation is b

Answer 1

Hmm, why not mix in a bit of (ba)sh? :-)

from subprocess import Popen, PIPE
cproc = Popen('cat | grep line', stdin=PIPE, stdout=PIPE, stderr=PIPE, shell=True)
out, err = cproc.communicate("this line has the word line in it")

BEWARE though:

• This only works on systems that use a Bourne Shell compatible shell (like most *nix'es)

• Usign shell=True and putting user input in the command string is a bad idea, unless you escape the user input first. Read the subprocess docs -> "Frequently Used Arguments" for details.

• This is ugly, non portable, non pythonic and so on...

EDIT: There is no need to use cat though, if all you want to do is grep. Just feed the input directly to grep, or even better, use python regular expressions.