Required in a loop

#!/bin/bash

required() {
    local terminate="0" missing="" var=""
    for var in "$@" ; do
        command -v "$var" >/dev/null 2>&1 || { missing="$var $missing" ; terminate="1"; }
    done
    if (( terminate )); then
        missing="${missing%"${missing##*[![:space:]]}"}"
        echo "I need $missing."
        exit 1 
    fi
}

required ack 'to shave' nitrogen # will exit here if missing