compgen

List all shell built-ins, aliases, functions, and executables that you could run

$ compgen -c

$ compgen -V COMPREPLY -c [str]

$ compgen -W "[apple orange banana]" [a]

$ compgen -a

$ compgen -A function

$ compgen -k

$ compgen -ac [ls]

$ compgen -u

compgen [-A action] [-bcdfghjksuv] [-G globpat] [-o option] [-W wordlist] [-F functionname] [-C commandname] [-X filterpat] [-P prefix] [-S suffix] [word]

-A action
    Generate completions based on action: alias, arrayvar, binding, builtin, command, directory, disabled, enabled, export, file, function, group, help, hostname, job, keyword, running, service, setopt, signal, stopped, user

-b
    Shortcut for -A builtin

-c
    Shortcut for -A command

-d
    Shortcut for -A directory

-f
    Shortcut for -A file

-g
    Shortcut for -A group

-j
    Shortcut for -A job

-k
    Shortcut for -A keyword

-s
    Shortcut for -A signal

-u
    Shortcut for -A user

-v
    Shortcut for -A export

-G globpat
    Filenames matching shell glob pattern globpat

-o option
    Completion behavior: bashdefault, default, dirnames, filenames, filenamedirs, nospace

-W wordlist
    Completions from colon-separated wordlist

-F functionname
    Completions from output of function functionname

-C commandname
    Completions from output of command commandname

-X filterpat
    Exclude matches with glob pattern filterpat; negate with '!' prefix

-P prefix
    Prepend prefix to each completion

-S suffix
    Append suffix to each completion

compgen is a Bash shell built-in command that generates lists of possible completions for command-line arguments, mimicking the behavior of the Tab key completion. It is primarily used within Bash's programmable completion system but can be invoked directly from the command line or scripts to output words matching specified criteria.

This tool is invaluable for shell scripting, custom completion functions, and debugging completion setups. By specifying options like -A for actions (e.g., aliases, functions, commands), -G for glob patterns, or -W for word lists, compgen filters and generates relevant completions against an optional word argument. For instance, it can list all available commands starting with 'ls' or all exported variables.

Unlike external tools, compgen leverages Bash's internal data structures for efficiency, making it fast for tasks like listing jobs, hostnames, or services. Output can be customized with prefixes (-P), suffixes (-S), and filters (-X). It's often paired with complete to define dynamic completions, enhancing interactive shell experience. While powerful, it's Bash-specific and unavailable in other shells like Zsh or Fish without emulation.

Bash built-in only; unavailable in non-Bash shells. Output depends on current shell state (e.g., jobs, variables). Multiple options may combine unpredictably. Not suitable for non-interactive scripts expecting stable output.

compgen -c ls
List commands starting with 'ls'.  compgen -A function
List all shell functions.  compgen -G '*.sh' -- '*.sh'
Match shell glob files.  compgen -W 'start stop restart' -- sta
Complete from wordlist matching 'sta'.

Introduced in Bash 1.14.0 (1994) as part of early programmable completion features. Evolved significantly in Bash 2.0+ with expanded -A actions and -o options. Core to Bash's completion system, maintained through Bash 5.x for enhanced scripting and interactivity.

complete(1), bash(1)