How to create script with auto-complete?

You'll have to create a new file:

/etc/bash_completion.d/foo

For a static autocompletion (--help / --verbose for instance) add this:

_foo() 
{
    local cur prev opts
    COMPREPLY=()
    cur="${COMP_WORDS[COMP_CWORD]}"
    prev="${COMP_WORDS[COMP_CWORD-1]}"
    opts="--help --verbose --version"

    if [[ ${cur} == -* ]] ; then
        COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
        return 0
    fi
}
complete -F _foo foo

• COMP_WORDS is an array containing all individual words in the current command line.
• COMP_CWORD is an index of the word containing the current cursor position.
• COMPREPLY is an array variable from which Bash reads the possible completions.

And the compgen command returns the array of elements from --help, --verbose and --version matching the current word "${cur}":

compgen -W "--help --verbose --version" -- "<userinput>"

Source

You can use the Programmable Completion. Have look at /etc/bash_completion and /etc/bash_completion.d/* for some examples.

Here is a complete tutorial.

Let's have an example of script called admin.sh to which you would like to have autocomplete working.

#!/bin/bash

while [ $# -gt 0 ]; do
  arg=$1
  case $arg in
    option_1)
     # do_option_1
    ;;
    option_2)
     # do_option_2
    ;;
    shortlist)
      echo option_1 option_2 shortlist
    ;;
    *)
     echo Wrong option
    ;;
  esac
  shift
done

Note the option shortlist. Calling the script with this option will print out all possible options for this script.

And here you have the autocomplete script:

_script()
{
  _script_commands=$(/path/to/your/script.sh shortlist)

  local cur
  COMPREPLY=()
  cur="${COMP_WORDS[COMP_CWORD]}"
  COMPREPLY=( $(compgen -W "${_script_commands}" -- ${cur}) )

  return 0
}
complete -o nospace -F _script ./admin.sh

Note that the last argument to complete is the name of the script you want to add autocompletion to. All you need to do is to add your autocomplete script to bashrc as

source /path/to/your/autocomplete.sh

or copy it to /etc/bash.completion.d