command-line-arguments.md

Python by Example: Command-Line Arguments

Scripts often need input from the command line. sys.argv is a list of strings: the first is the script name, the rest are the arguments you pass. It's simple but limited—for flags, help text, and validation, use argparse (next lesson).

What you'll learn:

• Accessing arguments with sys.argv
• sys.argv[0] is the script name

import sys

print("Script:", sys.argv[0])
print("Arguments:", sys.argv[1:])

if len(sys.argv) > 1:
    print("First arg:", sys.argv[1])

Everything after python script.py goes into sys.argv. The script path might be relative or absolute depending on how you invoked it.

To run this program:

$ python source/command-line-arguments.py foo bar
Script: source/command-line-arguments.py
Arguments: ['foo', 'bar']
First arg: foo

Tip: When run as a module (python -m mymodule), sys.argv[0] is the module path.

Try it: Run the script with different arguments and see how sys.argv changes.

Source: command-line-arguments.py

Next: Argparse