Bash script parse named arguments

parse.sh

#!/bin/bash
# My function header...
# Arguments:
#   "--uid" or "-u" -> uid - int - default: 0 - user id for...
#   "--gid" or "-g" -> gid - int - default: 0 - group id for...

# parse arguments
while [ $# -gt 0 ]; do
    case "${1%%=*}" in
    -u | --uid)
        arg_uid="${1#*=}"
        ;;
    -g | --gid)
        arg_gid="${1#*=}"
        ;;
    *)
        printf "Error: Invalid argument: '${1%%=*}' \n"
        exit 1
        ;;
    esac
    shift
done

# set argument defaults if necessary
if [ -z "$arg_uid" ]; then
    arg_uid=0
fi
if [ -z "$arg_gid" ]; then
    arg_gid=0
fi

echo "uid: $arg_uid"
echo "gid: $arg_gid"

Example Usage:

# ./parse.sh -u=23
uid: 23
gid: 0

# ./parse.sh -u=23 --gid=23
uid: 23
gid: 23

# ./parse.sh 12
Error: Invalid argument: '12'

# ./parse.sh -a=12
Error: Invalid argument: '-a'