Problems getting stdout back from shell command in Python

Question

I have a line of Unix Shell code:

lsusb | sed -e 's/.*ID \([a-f0-9]\+:[a-f0-9]\+\).*/\1/g'

I want to pass this to the shell from a script in Python and be able to catch the output in stdout as it would be displayed in the terminal after running that line of code.

However, I cannot get it to do it. I have tried:

• setting the variable I want to hold the output (x) equal to os.system(lsusb | sed -e 's/.*ID \([a-f0-9]\+:[a-f0-9]\+\).*/\1/g')

• setting x variable equal to subprocess.Popen() with all that mess being plugged in as a list and stdout being set to pipe and stderr and stdin being set to DEVNULL

• setting x equal to subprocess.check_output(), again with that whole line of code being passed in.

• setting x equal to the output of run()

I have also tried writing lsusb to a file and then passing that to sed instead of piping it. I have tried passing that entire line of code and setting all that equal to a variable in the shell and then setting the variable x equal to the shell variable. Finally, I have tried passing the output of this line of code to a file and reading the contents of that.

Everything I have tried will either give me:

• just 0

• these little square characters with 3 zeros and a 1 inside

• nothing

How can I get the data I am wanting passed to the x variable in a string format? This has been bugging me for a couple of days now and nothing is helping. If I need to use Python 3 that is okay, even though I prefer to use Python 2.

Thank you all for help! If you need any more information just ask and I will gladly edit them into the question here for all to see.

Thank you again!

Answer 1

There is a great answer about how to capture output from shell commands in Python at

Running shell command from Python and capturing the output

In this case, I suspect you need to use

subprocess.check_output("lsusb | sed -e 's/.*ID \([a-f0-9]\+:[a-f0-9]\+\).*/\1/g'", shell=True)

You need the shell=True otherwise Python will interpret the string as a single command, rather than a pipeline.