How To Make a Program Quit with “q” and Restore Console like “man” in Command Line Programming

In the world of command-line programming, efficiency and control are key. One such control is the ability to quit a program with a simple keystroke, like “q”, and restore the console to its previous state, similar to the man command. This article will guide you through the process of achieving this behavior using the less pager program in a Bash script.

Understanding the Basics

Before we dive into the specifics, it’s important to understand the basics of command-line programming. When you run a command, it produces output that is sent to the standard output (stdout). If the command encounters an error, it sends a message to the standard error (stderr). These outputs can be redirected using operators like | and >.

Introducing the less Pager Program

less is a program that allows you to view the output of a command in a scrollable format. It’s commonly used to view long outputs that don’t fit on a single screen. The most important feature of less for our purpose is that it can be exited by pressing “q”, which also restores the console to its previous state.

Using less to Quit a Program with “q”

To use less, you can pipe the output of your command to it using the | operator. Here’s how you can do it:

my_command_here | less

In this command, replace my_command_here with the actual command you want to run. The output of the command will be displayed in less, and you can scroll through it. Pressing “q” will exit less and return you to the console.

The | operator redirects the stdout of the command to less. This means that if your command produces any error messages, they won’t be displayed in less.

Including Error Messages in less

If you want to include error messages in less, you can use the |& operator instead of |:

my_command_here |& less

This command redirects both stdout and stderr to less, allowing you to see any error messages as well.

However, it’s important to note that |& is specific to Bash and may not work in other shells. If you’re writing a portable shell script, you can use the 2>&1 syntax to redirect stderr to stdout and then pipe it to less:

my_command_here 2>&1 | less

This command achieves the same result as |&, but it’s compatible with /bin/sh and other shells.

Conclusion

In command-line programming, the ability to control the flow of your program is crucial. By using the less pager program, you can make a program quit with “q” and restore the console to its previous state, similar to the man command. This gives you more control over your programs and makes them more user-friendly.

Remember to replace my_command_here with your actual command, and choose the right operator (|, |&, or 2>&1 |) based on your needs and the shell you’re using. Happy coding!