How to Create a CLI Tool with Python and argparse

Command-line interface (CLI) tools are powerful for automating tasks and creating user-friendly scripts. Whether you’re building internal utilities or open-source tools, Python makes it incredibly easy—especially with the built-in argparse module.

In this guide, you’ll learn how to create your own CLI tool using argparse with clear, beginner-friendly examples.

What Is a CLI Tool?

A CLI (Command-Line Interface) tool is a script or program that accepts user input via command-line arguments. Instead of a GUI, users interact with it by typing commands like:

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python tool.py –name Alice –greet

Why Use argparse?

• Built-in (no installation needed)
  
• Simple to use
  
• Automatically generates help messages
  
• Supports positional and optional arguments
  

Creating a Simple CLI Tool

Let’s create a basic greeting script that uses user-provided arguments:

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import argparse

parser = argparse.ArgumentParser(description=”A simple greeting CLI tool”)

parser.add_argument(‘–name’, type=str, help=’Your name’)

parser.add_argument(‘–greet’, action=’store_true’, help=’Print a greeting’)

args = parser.parse_args()

if args.greet and args.name:

    print(f”Hello, {args.name}!”)

else:

    print(“Use –greet and –name to get a greeting.”)

Run it like this:

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python greet.py –name Alice –greet

Output:

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Hello, Alice!

Positional vs Optional Arguments

• Positional: Required and order-dependent
  
• Optional: Use — prefix and can appear in any order
  

Example:

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parser.add_argument(‘filename’, help=’The file to process’)

Adding Default Values and Choices

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parser.add_argument(‘–lang’, choices=[‘en’, ‘es’], default=’en’, help=’Language option’)

This ensures users can only input en or es, with en as the default.

Auto Help Message

argparse automatically adds a –help option:

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python greet.py –help

Output:

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usage: greet.py [-h] [–name NAME] [–greet]

optional arguments:

  -h, –help     show this help message and exit

  –name NAME    Your name

  –greet        Print a greeting

Real-World Use Case: File Analyzer CLI

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import argparse

import os

def count_lines(filepath):

    with open(filepath, ‘r’) as file:

        return len(file.readlines())

parser = argparse.ArgumentParser(description=”File line counter”)

parser.add_argument(‘file’, help=’Path to the file’)

args = parser.parse_args()

if os.path.exists(args.file):

    print(f”{args.file} has {count_lines(args.file)} lines.”)

else:

    print(“File does not exist.”)

Practice Challenge

Create a CLI tool that takes a filename and a keyword, then counts how many times the keyword appears in the file.

Why It Matters

Creating CLI tools can:

• Automate repetitive tasks
  
• Improve productivity
  
• Help you contribute to developer tooling
  
• Showcase practical Python skills in portfolios or jobs
  

Take the Next Step

Now that you know how to create CLI tools with argparse, try building your own! You’ll not only deepen your Python knowledge but also create something genuinely useful.

🚀 For project-based Python learning, visit
👉 https://www.thefullstack.co.in/courses/

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