Enabling autocompletion for a custom script in zsh or bash

Autocompletion is a convenient feature in both Zsh and Bash shells that can save time and reduce typing errors. If you have a custom script that you frequently use, you may want to enable autocompletion for it. Here’s how to do it in both shells.

Zsh

Create a completion function for your script

Create a function that defines the possible options and arguments for your script. Save this function in a file with a name starting with an underscore, such as _myscript.

# _myscript completion function for Zsh
_myscript_completion() {
    local curcontext="$curcontext" state line
    typeset -A opt_args

    _arguments '1: :->command'

    case $state in
        (command)
            local -a commands=("option1" "option2" "option3")
            _describe -t commands 'myscript command' commands && ret=0
            ;;
    esac
}

compdef _myscript_completion myscript

Save the completion function file in a directory in the `FPATH` variable

Save the _myscript file in a directory where Zsh will look for autoloaded functions. One such directory is /usr/share/zsh/site-functions. Alternatively, you can create a new directory and add it to the FPATH variable in your .zshrc file.

# Add the custom directory to FPATH in .zshrc
fpath+=/path/to/custom/dir

Source the completion function file

If it doesn’t work for obscure reasons, you can just source your completion _myscript.

# Source the completion function file
source /path/to/_myscript

Now you should be able to use autocompletion for your custom script in Zsh. Type myscript followed by a space, and then press the Tab key to see the available options and arguments.

This is a hack

Because I encountered a persistent problem with autocompletion and didn’t want to keep editing my .zshrc file for every new script, I added the following lines to it:

for script in ~/.completion_scripts/_*; do
  script_name=${script:t}
  source ~/.completion_scripts/$script_name
done

Bash

Create a completion script for your script

Create a script that defines the possible options and arguments for your script. Save this script in a file with a name starting with an underscore, such as _myscript.

# _myscript completion script for Bash
_myscript_completion() {
    local cur prev opts
    COMPREPLY=()
    cur="${COMP_WORDS[COMP_CWORD]}"
    prev="${COMP_WORDS[COMP_CWORD-1]}"

    case "${prev}" in
        myscript)
            opts="option1 option2 option3"
            COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
            return 0
            ;;
        *)
            ;;
    esac
}

complete -F _myscript_completion myscript

Save the completion script file in a directory in the `PATH` variable

Save the _myscript file in a directory where Bash will look for executables. One such directory is /usr/local/bin. Alternatively, you can create a new directory and add it to the PATH variable in your .bashrc file.

# Add the custom directory to PATH in .bashrc
export PATH=$PATH:/path/to/custom/dir

Source the Bash completion scripts

Source the Bash completion scripts to load the autocompletion functionality in your current session.

# Source the Bash completion scripts
source /usr/share/bash-completion/bash_completion

Now you should be able to use autocompletion for your custom script in Bash. Type myscript followed by a space, and then press the Tab key to see the available options and arguments.

Zsh