如何不允许用户在getopts中同时指定两个选项？

#!/bin/bash

# 初始化选项记录变量
option_a=false
option_b=false

# 解析选项
while getopts "ab" opt; do
  case $opt in
    a)
      if $option_a; then
        echo "Error: Option -a is already specified."
        exit 1
      fi
      option_a=true
      ;;
    b)
      if $option_b; then
        echo "Error: Option -b is already specified."
        exit 1
      fi
      option_b=true
      ;;
    \?)
      echo "Invalid option: -$OPTARG"
      exit 1
      ;;
  esac
done

# 处理其他参数
shift $((OPTIND - 1))
# ...

# 示例结束