How to Build a Simple Python CLI with argparse

Create a friendly command-line greeting tool with argparse that accepts a positional name and optional flags for custom greetings and uppercase output.

Easy Python 3.9+ Aug 9, 2026 Automation & scripting 12 views 0 copies

argparse cli command-line automation scripting

Python code

30 lines

Python 3.9+

import argparse

def greet(name, greeting="Hello", uppercase=False):
    message = f"{greeting}, {name}!"
    return message.upper() if uppercase else message

if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        description="A simple greeting tool to demonstrate argparse basics."
    )
    parser.add_argument(
        "name",
        type=str,
        help="The person's name to greet."
    )
    parser.add_argument(
        "-g", "--greeting",
        type=str,
        default="Hello",
        help="Custom greeting word (default: Hello)."
    )
    parser.add_argument(
        "-u", "--uppercase",
        action="store_true",
        help="Print the greeting in uppercase."
    )
    
    args = parser.parse_args()
    result = greet(args.name, args.greeting, args.uppercase)
    print(result)

Output

stdout

$ python greet.py Ada
Hello, Ada!

$ python greet.py Ada -g Hi
Hi, Ada!

$ python greet.py Ada --uppercase
HELLO, ADA!

$ python greet.py --help
usage: greet.py [-h] [-g GREETING] [-u] name

A simple greeting tool to demonstrate argparse basics.

positional arguments:
  name                  The person's name to greet.

options:
  -h, --help            show this help message and exit
  -g GREETING, --greeting GREETING
                        Custom greeting word (default: Hello).
  -u, --uppercase       Print the greeting in uppercase.

How it works

The argparse module parses command-line arguments automatically, converting them into a namespace object. The parser.add_argument calls define the expected inputs: the first is a positional argument (required), while the others are optional flags with defaults. The store_true action sets args.uppercase to True when the flag is present, otherwise False. This pattern separates argument parsing from the greet function, keeping the logic testable and reusable. Using if __name__ == "__main__" guards the execution so the script can be imported without side effects.

Common mistakes

Omitting `args = parser.parse_args()` before accessing arguments
Confusing the order of positional vs. optional arguments in the help output
Forgetting to import argparse at the top of the script
Assuming a flag variable holds a string instead of a boolean when using `store_true`

Variations

Use `required=True` on an optional argument to force it, or rely on a positional.
Add a `--version` flag with `action="version"` for a quick version check.

Real-world use cases

A CI/CD script that takes a service name as input and optionally flags a dry-run mode.
A data pipeline CLI that accepts a file path and a `--verbose` flag to toggle logging.
A small internal tool that greets users with a custom message and optional uppercase for branding.

How to Build a Simple Python CLI with argparse

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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