Checking for lack of flags in bash

Question

If I were to do something like this to process arguments in bash, how would I check if there were no arguments? It doesn't seem to go to the *) case, but I'd still like to put a usage statement in there somewhere.

while getopts 'ias' flag; do
  case "${flag}" in
    i) ifl='true' ;;
    m) afl='true' ;;
    n) sfl='true' ;;
    *) error "Invalid option ${flag}" ;;
  esac
done

Answer 1

Before the while loop, do this

if (( $# == 0 )); then
    echo "you must specify one of -i or -a or -s"
    exit 1
fi

or, after the while loop, you can do this

if [[ $ifl != true && $afl != true && $sfl != true ]]; then
    echo "you must specify one of -i or -a or -s"
    exit 1
fi