How to Simulate the Linux More Command in Python: A Step-by-Step Guide
The more command in Linux is a handy tool for viewing large text files, displaying their contents one page at a time. But what if you could replicate this functionality in Python? Whether you're a Python enthusiast or someone looking to enhance your scripting skills, building a Python version of the more command is a great way to understand file handling, pagination, and user interaction in terminal applications.
In this tutorial, we’ll walk through the process of creating a Python script that mimics the more command. By the end, you’ll have a working tool that can handle large files and display their contents in a paginated format just like the original Linux command. Let's dive in and see how to bring this classic Unix functionality into your Python scripts!
Step-by-Step Breakdown of the Script
In this article, we’ll walk through how to build a Python script that simulates the more command in Linux. Our Python script will open a file, display its contents one page at a time, and allow the user to navigate through the file by pressing the space bar. Let’s break down the key parts of the code.
Step 1: Importing Required Libraries
We start by importing a few necessary libraries:
These libraries ensure we have access to terminal properties, can read user input, and manage file operations effectively.
Step 2: Getting Terminal Size and Handling Arguments
The next step is to retrieve the current size of the terminal using os.get_terminal_size(). We specifically focus on the number of lines available in the terminal window so that our script knows how many lines to display per page.
We also handle command-line arguments with sys.argv, ensuring that the script only runs if exactly one argument (the file name) is passed. If the wrong number of arguments is provided, the script throws an error using an assert statement.
Step 3: Checking if the File Exists
Before attempting to read the file, the script checks if the file exists using os.path.exists(). This ensures that the program doesn’t crash or throw confusing errors if the user provides an invalid file name. If the file doesn't exist, the script prints an appropriate error message.
Step 4: Reading and Splitting the File
If the file exists, the script opens the file and reads its content. The contents are split into individual lines using the split("\n") method. This allows us to process and display the file one line at a time, similar to how the more command works.
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Step 5: Paginating the Output
Here’s where the core functionality of the script lies. The script keeps track of how many lines have been displayed using the variables line and t_lines. It then compares the total lines shown (t_lines) to the terminal size (size). As long as the number of lines displayed doesn’t exceed the size of the terminal, the script continues printing lines.
Once the terminal is filled with text, the script pauses and waits for user input. At this point, it prints the percentage of the file that has been displayed to give the user an idea of their progress through the file.
Step 6: Handling User Input
To navigate through the file, the script listens for a keyboard event using the pynput library. Specifically, it waits for the user to press the space bar. Once the space bar is pressed, the script resets the line counter (t_lines) and resumes displaying the next set of lines.
Step 7: Error Handling and Conclusion
In case of any errors, such as a missing or incorrect file, the script handles the situation gracefully and displays an error message to the user.
Final Thoughts
This Python script offers a basic but functional imitation of the Linux more command, allowing users to view large text files one page at a time in a terminal environment. It demonstrates some useful techniques in Python such as handling command-line arguments, reading from files, interacting with terminal size, and capturing keyboard input in real-time.
With this tool, you can take better control of file output in Python, especially when dealing with large files that would otherwise flood the terminal screen. Try modifying the script further to add features such as scrolling backward, customizing the number of lines per page, or allowing different key commands to navigate the file.
The Complete Code
The following is the complete code for the Python script that simulates the Linux more command. This script allows you to read a file's contents one page at a time, providing a seamless way to navigate through large text files in your terminal.