Shell Scripting

Execute shell commands and scripts from Python.

Quick Start

import subprocess

# Simple command
result = subprocess.run(["ls", "-la"], capture_output=True, text=True)
print(result.stdout)

# With shell expansion
result = subprocess.run("echo $HOME", shell=True, capture_output=True, text=True)

Common Patterns

Run and capture output

def run_command(cmd: list[str]) -> tuple[str, str, int]:
    result = subprocess.run(cmd, capture_output=True, text=True)
    return result.stdout, result.stderr, result.returncode

stdout, stderr, code = run_command(["python", "--version"])

Check command success

def command_exists(cmd: str) -> bool:
    try:
        subprocess.run(
            ["which", cmd],
            capture_output=True,
            check=True
        )
        return True
    except subprocess.CalledProcessError:
        return False

Run with timeout

try:
    result = subprocess.run(
        ["long-running-command"],
        timeout=30,
        capture_output=True,
        text=True
    )
except subprocess.TimeoutExpired:
    print("Command timed out")

Pipe commands

# Equivalent to: cat file.txt | grep pattern
p1 = subprocess.Popen(["cat", "file.txt"], stdout=subprocess.PIPE)
p2 = subprocess.Popen(
    ["grep", "pattern"],
    stdin=p1.stdout,
    stdout=subprocess.PIPE,
    text=True
)
output = p2.communicate()[0]

Run in specific directory

result = subprocess.run(
    ["npm", "install"],
    cwd="/path/to/project",
    capture_output=True,
    text=True
)