Bash, no-arguments warning, and case decisions

if [[ $# -eq 0 ]] ; then
    echo 'some message'
    exit 0
fi

case "$1" in
    1) echo 'you gave 1' ;;
    *) echo 'you gave something else' ;;
esac

The Advanced Bash-Scripting Guide is pretty good. In spite of its name, it does treat the basics.