#!/bin/sh

: ${1:?first argument is required}
: ${2:?second argument is required}

#!/bin/sh
die() { echo "$@" >&2; exit 1; }
case ${1?} in
foo) test $# = 4 || die When first argument is foo, you must give 4 args;;
bar) test $# = 2 || die When first argument is bar, only give 2 args;;
*) ;;
esac