getopts ":a:" opt; do

xuanxuan_0176

#!/bin/bash

while getopts ":a:" opt; do
  case $opt in
    a)
      echo "-a was triggered, Parameter: $OPTARG" >&2
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      exit 1
      ;;
   
      echo "Option -$OPTARG requires an argument." >&2
      exit 1
      ;;
  esac
done


假如执行：
$ ./go_test.sh -a
Option -a requires an argument.
结果怎么是这样呢

deepalley

因为参数选项字符串是以冒号“：”开头的，这就告诉getopts，在处理需要value的参数（比如a）的时候，如果它没有带value（$ ./go_test.sh -a 【no value】），getopts就会把选项设置成冒号“：”，告诉你参数少东西，没带值

nuclearxin

If an option-argument is missing:

        * If the first character of optstring is a colon, the shell variable specified by name shall be set to the colon character and the shell variable OPTARG shall be set to the option chara
          acter found.

        * Otherwise,  the  shell  variable  specified by name shall be set to the question-mark character, the shell variable OPTARG shall be unset, and a diagnostic message shall be written to
          standard error. This condition shall be considered to be an error detected in the way arguments were presented to the invoking application, but shall not be an error in  getopts  proa
          cessing; a diagnostic message shall be written as stated, but the exit status shall be zero.

ctrl+c ctrl+v

wtuter

回复 1# xuanxuan_0176


    ：当optstring中的字母跟”:“时，表明该option可接参数，参数(argument)放在$OPTARG中；
      如果缺参数，且optstring是以”:“开头，则varname的值会是:，$OPTARG是该option，
      否则varname的值是?，$OPTARG是该option。