How to use `subprocess` command with pipes

python linux subprocess pipe
zuberuber picture zuberuber · Nov 11, 2012 · Viewed 238.1k times · Source

I want to use subprocess.check_output() with ps -A | grep 'process_name'. I tried various solutions but so far nothing worked. Can someone guide me how to do it?

Answer

Taymon picture Taymon · Nov 11, 2012

To use a pipe with the subprocess module, you have to pass shell=True.

However, this isn't really advisable for various reasons, not least of which is security. Instead, create the ps and grep processes separately, and pipe the output from one into the other, like so:

ps = subprocess.Popen(('ps', '-A'), stdout=subprocess.PIPE)
output = subprocess.check_output(('grep', 'process_name'), stdin=ps.stdout)
ps.wait()

In your particular case, however, the simple solution is to call subprocess.check_output(('ps', '-A')) and then str.find on the output.

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