Bash completion for all files in all subdirectories of a directory

subdir-files-completion.sh

function _subfiles() {
    COMPREPLY=()
    local CUR FILES
    CUR="${COMP_WORDS[COMP_CWORD]}"
    FILES="$(find ${_COMP_DIR}/* -type f|awk -F ${_COMP_DIR}/ '{print $2}')"
    COMPREPLY=( $(compgen -W "${FILES}" -- ${CUR}) )
    return 0
}

this TAB-completion bash function searches for all files that are children of $_COMP_DIR.

This is not generic because $_COMP_DIR will be searched base on it's current value, not the one when the completion function was defined or specifed to bash with complete -F _subfiles somefunction. So it will search whichever directory the current value of $_COMP_DIR is at the time the function is called (i.e. when TAB is pressed to complete for whichever function it's bound to).

So, you will need to copy this function for different specific completions (say, your key files):

export KEY_DIR=~/key
function _keyfiles() {
    COMPREPLY=()
    local CUR KEYS
    CUR="${COMP_WORDS[COMP_CWORD]}"
    KEYS="$(find ${KEY_DIR}/* -type f|awk -F ${KEY_DIR}/ '{print $2}')"
    COMPREPLY=( $(compgen -W "${KEYS}" -- ${CUR}) )
    return 0
}