Manual Pages  — GETOPT

args=getopt abo: $*
# you should not use getopt abo: "$@" since that would parse
# the arguments differently from what the set command below does.
if [ $? -ne 0 ]; then
        echo 'Usage: ...'
        exit 2
fi
set -- $args
# You cannot use the set command with a backquoted getopt directly,
# since the exit code from getopt would be shadowed by those of set,
# which is zero by definition.
while :; do
        case "$1" in
        -a|-b)
                echo "flag $1 set"; sflags="${1#-}$sflags"
                shift
                ;;
        -o)
                echo "oarg is '$2'"; oarg="$2"
                shift; shift
                ;;
        --)
                shift; break
                ;;
        esac
done
echo "single-char flags: '$sflags'"
echo "oarg is '$oarg'"

This code will accept any of the following as equivalent:

cmd -aoarg file1 file2
cmd -a -o arg file1 file2
cmd -oarg -a file1 file2
cmd -a -oarg -- file1 file2