PATH=/bin:/usr/bin

if test $# -ne 2
then
    echo usage: $0 pattern file >&2
    exit 1
fi

case "`grep "$@" | wc -l`" in
    0)
        # either a grep error (already output to stderr) or no match
        exit 1
        ;;
    1)
        # success
        grep "$@"
        exit 0
        ;;
    *)
        echo $0: too many matches >&2
        exit 1
        ;;
esac