Building Your Own CLI (Command Line Interface) Tool with Python on Linux

Table of Contents

  1. Introduction
  2. Prerequisites
  3. Setup
  4. Creating the CLI Tool
  5. Defining Commands
  6. Executing Commands
  7. Adding Arguments
  8. Handling Errors
  9. Conclusion

Introduction

In this tutorial, we will learn how to build our own Command Line Interface (CLI) tool using Python on a Linux system. A CLI tool allows users to interact with a program or script through a command-line interface, providing a more efficient and flexible way of executing tasks. By the end of this tutorial, you will have a good understanding of how to create a CLI tool and perform various operations using it.

Prerequisites

Before starting this tutorial, you should have:

  • Basic knowledge of Python programming language
  • Familiarity with the Linux operating system
  • Python installed on your Linux system

Setup

To begin, let’s ensure that you have Python installed on your Linux system. Open the terminal and run the following command to check the Python version:

   python --version

If Python is not installed, you can install it using the package manager of your Linux distribution. For example, on Ubuntu, you can use the following command:

   sudo apt install python

Once you have Python installed, we can proceed to create our CLI tool.

Creating the CLI Tool

  1. Open a text editor and create a new file called cli_tool.py.

  2. Start the file with a shebang line to specify the interpreter:

    #!/usr/bin/env python

  3. Import the necessary modules:

    import sys
import argparse

  4. Define a main function that will be the entry point of our CLI tool:

    def main():
 # Your code here
 pass
   
if __name__ == '__main__':
 main()
  5. Save the file.

Defining Commands

Now, let’s define the commands that our CLI tool will support. We’ll use the argparse module to define and parse command-line arguments.

  1. Inside the main function, create an instance of the argparse.ArgumentParser class:

    def main():
 parser = argparse.ArgumentParser(description='CLI Tool')

  2. Add a command using the add_subparsers method of the parser object:

    def main():
 parser = argparse.ArgumentParser(description='CLI Tool')
   
 # Add a subparser for the command 'hello'
 hello_parser = parser.add_subparsers(dest='command')
   
 hello_parser.add_parser('hello', help='Print hello message')

  3. Save the file.

Executing Commands

Next, let’s implement the execution logic for each command.

  1. Inside the main function, add an if statement to check the value of the command variable:

    def main():
 parser = argparse.ArgumentParser(description='CLI Tool')
 hello_parser = parser.add_subparsers(dest='command')
 hello_parser.add_parser('hello', help='Print hello message')
   
 args = parser.parse_args()
   
 if args.command == 'hello':
     print('Hello, world!')

  2. Save the file.

Adding Arguments

Now, let’s add arguments to our commands to make them more flexible.

  1. Inside the hello subparser, add an argument using the add_argument method:

    def main():
 parser = argparse.ArgumentParser(description='CLI Tool')
 hello_parser = parser.add_subparsers(dest='command')
 hello = hello_parser.add_parser('hello', help='Print hello message')
   
 hello.add_argument('name', help='Name of the person to greet')

  2. Modify the execution logic to use the value of the name argument:

    def main():
 parser = argparse.ArgumentParser(description='CLI Tool')
 hello_parser = parser.add_subparsers(dest='command')
 hello = hello_parser.add_parser('hello', help='Print hello message')
 hello.add_argument('name', help='Name of the person to greet')
   
 args = parser.parse_args()
   
 if args.command == 'hello':
     print(f'Hello, {args.name}!')

  3. Save the file.

Handling Errors

Let’s handle errors when the user provides invalid or missing arguments.

  1. Add an if statement to check if the name argument is provided:

    def main():
 parser = argparse.ArgumentParser(description='CLI Tool')
 hello_parser = parser.add_subparsers(dest='command')
 hello = hello_parser.add_parser('hello', help='Print hello message')
 hello.add_argument('name', help='Name of the person to greet')
   
 args = parser.parse_args()
   
 if args.command == 'hello':
     if args.name:
         print(f'Hello, {args.name}!')
     else:
         print('Please provide a name.')

  2. Save the file.

Conclusion

Congratulations! You’ve created a basic CLI tool in Python. This tutorial guided you through defining and executing commands, adding arguments, and error handling. This serves as a foundation for building more complex CLI tools. Keep practicing and experimenting with different commands and functionalities to enhance your skills. Happy coding!

Published:

Related Articles