Bashでオプション引数をとる方法

下記の例で、変数A, B, Cにbashからオプション引数を割り当てる方法示します。

#!/bin/bash

set -e
set -o pipefail

OPT=`getopt a:b:c: $*`
set -- $OPT

for i; do
  case $i in
    --) shift; break ;;
    -a) A=$2; shift; shift;;
    -b) B=$2; shift; shift;;
    -c) C=$2; shift; shift;;
  esac
done

# check if A, B and C are properly given from option.
if [ -z "$A" ]; then echo "A is not specified"; exit; fi
if [ -z "$B" ]; then echo "B is not specified"; exit; fi
if [ -z "$C" ]; then echo "C is not specified"; exit; fi