How to Properly Pipe Commands Using Python's `subprocess` Module?

How to Use Pipes with the subprocess Command

When working with the subprocess module, there may arise scenarios where you need to use pipes to connect multiple commands. This question explores the challenge of employing subprocess.check_output() with the following command:

ps -A | grep 'process_name'

Answer

To use a pipe with subprocess, the shell=True argument can be employed. However, using shell=True poses security concerns and should be approached with caution. A better approach involves creating the ps and grep processes separately and piping the output from one into the other:

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

In the specific scenario mentioned, a simpler solution would be to invoke subprocess.check_output(('ps', '-A')) and use str.find on the output.

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