关于getopts中的内置变量OPTIND问题

liboby

各位高手帮帮忙啊
我写的一个关于getopts的简单脚本在系统中运行后显示无法找到$OPTIND这个内置变量，请问下要怎么解决啊，下面是我的脚本代码
while getopts "y:z:" opt;
do
case $opt in
        X )opt='-x set';;
        Y ) yopt="-y set and called with $OPTARG";;
        Z ) zopt="-z set and called with $OPTARG";;
        \? ) echo 'USAGE: getopts.sh [-x] [-y arg] [-z arg ] file ...'
          exit 1
  esac
done
shift $($OPTIND - 1)
echo ${xopt: -'did not use -x'}
echo ${yopt: -'did not use -y'}
echo ${zopt: -'did not use -z'}
echo "Remaining command-line arguments are:"
for f in "$@"
do
  echo -e "$f"
done