How Can I Run Shell Commands and Capture Their Output in Python?

Running Shell Commands and Capturing Output

The task of executing shell commands programmatically and capturing their output as a string can be accomplished with the help of Python's subprocess module.

check_output Function (Python 2.7 and Above)

For the simplest approach in officially maintained Python versions, utilize the check_output function:

import subprocess

output = subprocess.check_output(['ls', '-l'])
print(output) # Output: b'total 0\n-rw-r--r--  1 memyself  staff  0 Mar 14 11:04 files\n'

run Function (Python 3.5 and Higher)

In Python 3.5 , the run function provides a more flexible and modern approach:

import subprocess

result = subprocess.run(['ls', '-l'], stdout=subprocess.PIPE)
print(result.stdout.decode('utf-8')) # Output: 'total 0\n-rw-r--r--  1 memyself  staff  0 Mar 14 11:04 files\n'

Popen Constructor (All Versions)

For extended compatibility and advanced functionality, use the low-level Popen constructor. With communicate, you can capture output and pass input:

import subprocess

p = subprocess.Popen(['ls', '-a'], stdout=subprocess.PIPE)
output, _ = p.communicate()
print(output) # Output: b'.\n..\nfoo\n'

Notes

Shell Command Execution (shell=True Argument)

By default, the functions execute single programs. To execute complex shell commands, set shell=True. However, this raises security concerns.

Input Handling

To pass input via stdin, specify the input keyword argument in run or Popen.

Error Handling

For proper error handling, use check_output with stdout=subprocess.STDOUT or Popen with stderr=subprocess.STDOUT. Alternatively, check the subprocess returncode.

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