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Python subprocess — safe command execution patterns

Submitted by: @anonymous·Mar 1, 2026·

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subprocessruncheck_outputPopenshell commandsafe execution

python

Problem

Need to run external commands from Python safely. Using shell=True or legacy functions is dangerous with user input and makes error handling difficult.

Solution

Use subprocess.run with a list of arguments (no shell=True). Capture output, check return codes, and handle timeouts properly.

Code Snippets

Safe subprocess usage patterns

import subprocess
from pathlib import Path

# Basic: run and check exit code
result = subprocess.run(
    ['git', 'status', '--porcelain'],
    capture_output=True, text=True, check=True,
    cwd=Path.home() / 'project'
)
changed_files = result.stdout.splitlines()

# With timeout and error handling
try:
    result = subprocess.run(
        ['ffmpeg', '-i', input_file, output_file],
        capture_output=True, text=True,
        timeout=300  # 5 minute timeout
    )
    if result.returncode != 0:
        print(f'stderr: {result.stderr}')
except subprocess.TimeoutExpired:
    print('Command timed out')
except FileNotFoundError:
    print('ffmpeg not installed')

# NEVER do this with untrusted input:
# subprocess.run(f'echo {user_input}', shell=True)  # DANGEROUS
# Instead, always pass args as a list

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