The compgen command in Linux is a built-in feature of the Bash shell used to display a list of available commands, functions, aliases, and reserved words.

It’s part of the programmable completion system and is mainly used to introspect what the shell knows.

For example, running compgen -c outputs all executable commands that the shell can auto-complete, while compgen -b shows all built-in shell commands. This makes it a powerful tool for users exploring available capabilities or writing shell scripts that rely on specific command environments.

In addition to command discovery, compgen supports filtered output based on prefixes. Running compgen -c ls will return commands starting with “ls,” such as ls, lsof, and lsblk.

This is helpful for quickly identifying related commands or verifying whether a command exists before using it in a script.

Since compgen works directly with the shell’s command hash table, it reflects real-time availability based on the current user’s $PATH and environment.

For example, The command pipeline compgen -c | wc -l is a powerful one-liner in Linux that combines two tools to count the number of available commands in the current shell session.

The first part, compgen -c, lists every command the Bash shell recognizes—this includes binaries, aliases, functions, and built-ins that are accessible within your environment. It’s a complete reflection of your command landscape based on your $PATH and shell configuration.

The second part of the pipeline, | wc -l, counts the number of lines output by compgen -c, effectively returning the total number of commands.

In the screenshot, the output is 4711, which means the terminal environment has 4,711 recognized commands available for execution.

This includes everything from system utilities and installed packages to user-defined functions, making it an excellent benchmark of system complexity and capability.

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