Processing command-line arguments in Bash

getargs.bash

#!/bin/bash

die() { echo "$1"; exit 1; }

usage() {
cat <<EOF
Usage: getargs [--help] [OPTION...] ARGUMENT...

Example usage of useful conventions for command-line argument parsing.

Options:
  -h, --help            display this help message
  -a, --alpha           set alpha to true
  -b, --beta=VAL        set beta to VAL

Arguments:
  ARGUMENT              one or more nonsense arguments

EOF
}

# Default values
alpha=false
beta=

# Option parsing
while [ $# -gt 0 ]; do
    case "$1" in
        --*=*)      a="${1%%=*}"; b="${1#*=}"; shift; set -- "$a" "$b" "$@" ;;
        -h|--help)  usage; exit 0; shift ;;
        -a|--alpha) alpha=true; shift ;;
        -b|--beta)  beta="$2"; shift 2 ;;
        --)         shift; break ;;
        -*)         usage; die "Invalid option: $1" ;;
        *)          break ;;
    esac
done
# Deal with positional arguments here: $1, $2, etc.

echo "alpha: $alpha;   beta: $beta   args: $@"

# $ ./getargs.sh
# alpha: false;   beta:    args: 
# $ ./getargs.sh -a
# alpha: true;   beta:    args: 
# $ ./getargs.sh -ab
# Usage: getargs [--help] [OPTION...] ARGUMENT...
#
# [...]
#
# Invalid option: -ab
# $ ./getargs.sh --alpha
# alpha: true;   beta:    args: 
# $ ./getargs.sh --beta=1
# alpha: false;   beta: 1   args: 
# $ ./getargs.sh --beta 1
# alpha: false;   beta: 1   args: 
# $ ./getargs.sh --alpha --beta 1
# alpha: true;   beta: 1   args: 
# $ ./getargs.sh -a -b 1
# alpha: true;   beta: 1   args: 
# $ ./getargs.sh -a -b 1 one two
# alpha: true;   beta: 1   args: one two