Parses long & short flags in a single block

flag-parser.sh

#!/bin/bash

DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd )"

# ----- defaults -----
SOME_FLAG=false

# ----- arg parsing -----

show_help(){
  cat <<EOF
Usage: [options]
-h| --help          show this help text
-sf| --some-flag    do something
EOF
}

while :; do
     case $1 in
         -h|-\?|--help)
             show_help
             exit
             ;;
         -sf|--some-flag)
             SOME_FLAG=true
             ;;
         --) # End of all options.
             shift
             break
             ;;
         -?*)
            printf 'WARN: Unknown option (ignored): %s\n' "$1" >&2
            ;;
        *)  # Default case: No more options, so break out of the loop.
            break
    esac

    shift
done

# Handle positional arguments
if [ -n "$*" ]; then
    echo "Extra arguments -- $*"
    echo "Try '-h' for more information."
    exit 1
fi
# ----- end arg parsing -----

set -u

if [ $SOME_FLAG = true ]; then
    echo "do something"
fi