getopt.bash

#!/usr/bin/env bash

# Take all the positional parameters ($*) and normalize them
# -ab1 becomes -a -b 1 or -b1 -a becomes -b 1 -a
# Note that the : after b means that it should have a value instead of
# just being the boolean flag that a is.
args=`getopt ab: $*`

# Rewrite ARGV with the output of getopt
set -- $args

# i refers to each positional parameter
for i do
  case "$i" in
    -a)
      a_defined=0;
      # Remove the current option from ARGV so that the next one is
      # available
      shift;;
    -b)
      # Since this has an actual value, that needs to be shifted
      # off ARGV along with -b
      b_value=$2; shift;
      shift;;
    --)
      shift; break;;
  esac
done

getopts.bash

#!/usr/bin/env bash

while getopts "ab:" opt; do
  declare "opt_$opt=${OPTARG:-0}"
done