linux命令行参数getopts参数二选一

die () {
    echo "ERROR: $*. Aborting." >&2
    exit 1
}

opta=false
optb=false
while getopts "a:b:" opt; do
  case $opt in
      a ) $optb && die "Cannot specify option a after specifying option b"
          opta=true
          a = $OPTARG 
          ;;
      b ) $opta && die "Cannot specify option b after specifying option a"
          optb=true
          b = $OPTARG 
          ;;
      \?) die "Invalid option: -$OPTARG. Abort"
          ;;
  esac
done

if [ $a ];then
    echo $a 
else
    echo $b
fi