enable

Print the list of builtins

$ enable

$ enable -n [command]

enable [-a] [-n] [name ...]

-a
    List all built-in commands, including those currently enabled and disabled.

-n
    If name(s) are provided, disable the specified built-in command(s). If no name is given, list all currently disabled built-in commands.

name ...
    One or more names of built-in commands to enable or disable. If no option is specified, the command(s) will be enabled.

The enable command is a shell built-in, primarily found in shells like bash and zsh. Its fundamental purpose is to manage the availability of other shell built-in commands. Built-in commands are executed directly by the shell, offering performance benefits over external executables. By default, most built-ins are enabled.

Users can leverage enable to temporarily disable a specific built-in, preventing its execution and potentially allowing an external command or a shell function with the same name to take precedence. Conversely, it can re-enable a built-in that was previously disabled. This capability is invaluable for debugging, overriding default shell behavior with custom scripts, or handling scenarios where a specific external utility needs to be prioritized over a built-in. The command can also be used to list currently enabled or disabled built-ins, providing insight into the shell's command processing environment.

enable is a shell built-in, not an external executable. Its behavior can vary slightly between different shells (e.g., bash vs. zsh). Changes made with enable are typically session-specific and will revert upon shell exit unless explicitly saved in a shell configuration file (e.g., .bashrc). Disabling critical built-ins might impact fundamental shell functionality. It affects only built-ins; it does not disable external commands or shell functions.

It's crucial to understand that enable is a shell built-in. This means it is an integral part of the shell itself, not a separate program located in directories like /bin or /usr/bin. Therefore, you won't find a dedicated manual page for enable by running man enable; instead, its documentation is typically included within the manual page of the shell it belongs to (e.g., man bash for bash users).

When you enter a command, the shell resolves it based on a specific order of precedence: aliases are checked first, followed by shell functions, then built-in commands, and finally external executables found in the PATH. Disabling a built-in with enable -n effectively removes it from the built-in step, causing the shell to proceed to search for an external command or function if one exists with the same name.

The concept of built-in commands has been integral to Unix shells since their inception, providing efficiency by executing commands directly within the shell process. The specific enable command, allowing dynamic control over these built-ins, emerged as shells evolved into more sophisticated and programmable environments like bash and zsh. Its development reflects a desire for greater flexibility and fine-grained control over shell behavior, enabling advanced scripting and customization that was not feasible in earlier, simpler shell designs.

builtin(1), type(1), help(1), command(1)