Programmable completion

Simple completion using function

_mycompletion() {
    local command_name="$1" # not used in this example
    local current_word="$2"
    local previous_word="$3" # not used in this example
    # COMPREPLY is an array which has to be filled with the possible completions
    # compgen is used to filter matching completions
    COMPREPLY=( $(compgen -W 'hello world' -- "$current_word") )
}    
complete -F _mycompletion mycommand

Usage Example:

$ mycommand [TAB][TAB]
hello world
$ mycommand h[TAB][TAB]
$ mycommand hello

Simple completion using function

Simple completion for options and filenames