How to Capture Output of Command in Python Easily

Use the subprocess.run() function with capture_output=True to run a command and capture its output in Python. The output is available as stdout in bytes, which you can decode to a string.

Syntax

The basic syntax to capture the output of a command in Python is:

result = subprocess.run([command, arg1, arg2], capture_output=True, text=True)

Here:

• command and its arguments are passed as a list.
• capture_output=True tells Python to capture stdout and stderr.
• text=True makes the output a string instead of bytes.
• result.stdout contains the command's output.

python

import subprocess

result = subprocess.run(['echo', 'Hello, world!'], capture_output=True, text=True)
print(result.stdout)

Output

Hello, world!

Example

This example runs the ls command (or dir on Windows) and captures its output as a string. It then prints the output.

python

import subprocess
import platform

command = ['ls'] if platform.system() != 'Windows' else ['cmd', '/c', 'dir']

result = subprocess.run(command, capture_output=True, text=True)
print('Command output:')
print(result.stdout)

Output

Command output:
<list of files and folders in current directory>

Common Pitfalls

Common mistakes when capturing command output include:

• Not using capture_output=True, so output is not captured.
• Forgetting text=True, which makes output bytes instead of string.
• Passing the command as a single string instead of a list, which can cause errors.

Example of wrong and right usage:

python

# Wrong: output not captured
import subprocess
subprocess.run(['echo', 'Hello'])

# Right: output captured and decoded
result = subprocess.run(['echo', 'Hello'], capture_output=True, text=True)
print(result.stdout)

Output

Hello

Quick Reference

Parameter	Description
capture_output=True	Captures stdout and stderr of the command
text=True	Returns output as string instead of bytes
args as list	Pass command and arguments as a list for safety
result.stdout	Contains the captured standard output
result.stderr	Contains the captured error output

Key Takeaways

Use subprocess.run() with capture_output=True to capture command output.

Add text=True to get output as a readable string.

Always pass the command and its arguments as a list.

Access the output via result.stdout after running the command.

Be careful to capture output; otherwise, it prints directly to the console.