python getoutput() equivalent in subprocess

Question

I want to get the output from some shell commands like ls or df in a python script. I see that commands.getoutput('ls') is deprecated but subprocess.call('ls') will only get me the return code.

I'll hope there is some simple solution.

score 116 · Accepted Answer · edited Dec 02 '19 at 11:45

116

Use subprocess.Popen:

import subprocess
process = subprocess.Popen(['ls', '-a'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = process.communicate()
print(out)

Note that communicate blocks until the process terminates. You could use process.stdout.readline() if you need the output before it terminates. For more information see the documentation.

edited Dec 02 '19 at 11:45

Balaji Dubey

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answered Jul 11 '11 at 23:03

Michael Smith

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The correct current doc link for the Python 2.7 version of `subprocess` examples is: http://docs.python.org/library/subprocess.html#replacing-older-functions-with-the-subprocess-module ; for Python 3.2, http://docs.python.org/py3k/library/subprocess.html#replacing-older-functions-with-the-subprocess-module – Ned Deily Jul 11 '11 at 23:09
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You probably need to replace the subprocess.communicate() with process.communicate() - you may also need the subprocess exit code by doing process.returncode – Cinquo Jul 11 '11 at 23:11
I didn't notice that I had written subprocess instead of process. Fixed. – Michael Smith Jul 11 '11 at 23:13
what types are out and err? are they regular strings or are they arrays or dictionaries? – scottysseus Aug 06 '13 at 18:02
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Works fine for `out` but `err` will be uninitialized and the error output printed to the screen. You'll have to specify `stderr=subprocess.PIPE` in addition to `stdout` to get the standard error. – Gerrit-K Aug 20 '14 at 19:09
What type is "out"? It looks like it's an object of some type because I cannot write it to a file like it's a string `subprocess.Popen(["echo", out, ">>", "/home/ec2-user/output_test.sh"], stdout=subprocess.PIPE)` – Kyle Bridenstine Jan 09 '19 at 21:43

score 56 · Answer 2 · answered Jun 26 '13 at 21:09

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For Python >= 2.7, use subprocess.check_output().

http://docs.python.org/2/library/subprocess.html#subprocess.check_output

answered Jun 26 '13 at 21:09

knite

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Technically, it should be `subprocess.check_output(cmd, shell=True)`. – Cerin Apr 18 '16 at 17:23
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What is the difference shell True or False? – Ricky Wilson Jul 31 '17 at 16:11
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I think it enables "shell specific features" like file globbing, piping etc... – Rafael T Sep 20 '17 at 13:41
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@RickyWilson commands baked into the shell like 'dir' (or 'ls') will give you an error and not be found unless you pass in shell=True, along with the other shell-specific features like piping as stated above. Otherwise the subprocess cmd list should be a valid filepath and its arguments. Also when shell=True you may incur a max string length of the command allowed, depending on platform, whereas shell=False would allow a longer command to be digested than a shell would normally allow to be typed in manually. – Jordan Stefanelli Oct 14 '18 at 09:39

score 11 · Answer 3 · answered Jul 12 '18 at 17:44

To catch errors with subprocess.check_output(), you can use CalledProcessError. If you want to use the output as string, decode it from the bytecode.

# \return String of the output, stripped from whitespace at right side; or None on failure.
def runls():
    import subprocess
    try:
        byteOutput = subprocess.check_output(['ls', '-a'], timeout=2)
        return byteOutput.decode('UTF-8').rstrip()
    except subprocess.CalledProcessError as e:
        print("Error in ls -a:\n", e.output)
        return None

python getoutput() equivalent in subprocess

3 Answers3

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