Getopts in the shell.

by Francis_hao Jul 5,2017

Getopts is a built-in command for the shell.

Overview

Getopts optstringname [args]
Optind,optarg,opterr

Describe

Getopts is used by the shell program to analyze positional parameters,optstring contains the option characters that need to be recognized, if the character followed by a colon, indicating that the word check requires a parameter, the parameters need to be separated by a space. Colons and question marks cannot be used as option characters.

Getopts each time it is called, it places the next option character on the variable name and initializes it if the name does not exist.

The variable optind is the index of the next positional parameter to be processed, with an initial value of 1. The shell does not automatically reset the Optind, and if you want to analyze the position parameters again, you need to reset the optind manually.

When a parameter is required for an election, getopts places the argument in the variable optarg,

When all positional parameter parsing is complete, getopts exits and returns a value greater than 0, Optind becomes the first index of the position parameter that is not the option, and name is set to '? '.

By default, getopts parses the incoming positional parameters, but if args has a value, only the parameters in args are parsed, and args only supports forms such as-ABC.

If an error is encountered, getopts prints out an error message, but if the optstring first character is a colon, or the variable opterr is set to 0 (this item simply does not print an error message and does not have a value of Optarg after an error), it enters silent mode. Error messages are not printed. There are usually two types of errors encountered:
1. Invalid option, name will be set to '? ' at this time. In silent mode, this invalid option is placed in Optarg. Non-silent mode, prints error messages, and unset optarg.
2, the option required parameters are not provided, in silent mode, name will be set to ': ', invalid option will be placed in Optarg. Non-silent mode, name is set to '? ', unset optarg and print error message.

Getopts returns True (0) If an option is encountered (whether or not valid), returns False if it encounters an end or generates an error.

Example

Example from reference "2"

#!/bin/sh whilegetopts:Ab:C:OPTION; Do Case$OPTIONinch A)Echo "Get Option A" ;; B)Echo "Get option B and parameter is $OPTARG" ;; C)echo"get option C and parameter is $OPTARG" ;; ?) Echo "Get a non option $OPTARG and option is $OPTION" ;; Esac Done

A running instance

Where-A and-B are the correct options, and the-P and-C respectively correspond to the two cases of the error option.

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Reprinted from: http://www.cnblogs.com/yinghao1991/p/7123550.html

Reference

"1" Man bash

"2" D. tes. Linux and Unix shell Programming Guide. Mechanical industry press. 2000-1

Getopts in the shell.