Application of getopts in shell

The format of the statement is: Getopts The general format is:

Getopts option_string Variable

Where option_string contains a valid single-character option. If the getopts command finds a hyphen on the command line, it is compared with the word descriptor option_string after the hyphen. If there is a match, set the value of the variable variable to this option

。 If there is no match, then the variable is set to?. When Getopts discovers that there are no characters behind the hyphen, it returns a nonzero status value. The shell program can use the return value of the getopts to create a loop.

Sometimes the option also has a value, and the getopts command also supports this feature. You need to add a colon to the option_string after you select the letter. When the getopts command finds a colon, the value is read from the command line after the option. If the value exists, then there will be a special variable in the Optarg. If the value does not exist, the getopts command holds a question mark in the Optarg and displays a message on the standard error output.

Optstring option string that will match one by one

VarName options for each successful match

ARG parameter list, which takes a command-line argument list when it is not written

$OPTIND special variable, option index, incremented one by one, with an initial value of 1

$OPTARG special variable, option argument, with different values in different cases

Rule 1: When optstring begins with ":", getopts distinguishes between invalid option error and miss option argument error.

Invalid option, the varname will be set to, $OPTARG is the problem of option;
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Here's the actual test:

  [[email protected] mnt]# vim getopt.sh   1 #!/bin/bash                                                                      2 while getopts  "A:B:C: def " what; do  3   case  $what  in  4      a)   5       echo  "this is -a the  arg is !  $OPTARG "     6        ;;   7     B)   8       echo  "This is -b the arg is !  $OPTARG "     9        ;;  10     C)  11       echo  "this  is -c the arg is !  $OPTARG "    12        ;;  13     D)  14         echo   "this is -d the arg is !  $OPTARG"  15          ;;  16     \?)  17       echo  "invalid option: -$OPTARG"      18       ;;  19   esac 20 done

Note A:b:c:def We first verify that the following ": "

A b c is followed by:

[Email protected] mnt]#./getopt.sh-a
./getopt.sh:option requires an argument--a
Invalid option:-

[Email protected] mnt]#./getopt.sh-c
./getopt.sh:option requires an argument-C
Invalid option:-

[Email protected] mnt]#./getopt.sh-c Hello
This is-c, the ARG is! Hello./getopt.sh:option requires an argument-C
Invalid option:-

[[email protected] mnt]#./getopt.sh-b ni
This is-b, the ARG is! Ni

D E F no colon

[Email protected] mnt]#./getopt.sh-d
This is-d, the ARG is!

[Email protected] mnt]#./getopt.sh-d Hello
This is-d, the ARG is!

There are two parameters-A and the following Hello

It can be seen that there is a colon he will force the detection of the following parameters to refer to, no error will be. such as a B C and D does not have: No, he doesn't have a value that the system thinks must be stored in the variable $optarg.

now look at the plot with the first colon

  1 #!/bin/bash                                                                     2  while getopts  ": A:b:c:def"  what; do  3   case  $what  in   4     a)   5       echo  "this is -a the arg is !  $OPTARG"      6        ;;   7     B)   8       echo  "this is -b the arg is !  $OPTARG"      9       ;;  10     C)  11       echo  "this  is -c the arg is !  $OPTARG "    12        ;;  13     D)  14         echo   "this is -d the arg is !  $OPTARG"  15          ;;  16     \?)  17       echo  "invalid option: -$OPTARG"      18       ;;  19   esac 20 done

[Email protected] mnt]#./getopt.sh-a
[Email protected] mnt]#./getopt.sh-b
[Email protected] mnt]#./getopt.sh-c
[Email protected] mnt]#./getopt.sh-d
This is-d, the ARG is!

[Email protected] mnt]#./getopt.sh-a Hello
This is-a, the ARG is! Hello
[Email protected] mnt]#./getopt.sh-b wo
This is-b, the ARG is! Wo

You can see that the system now ignores the following error message-a-b-C would have been to add the parameter value or error, but the head to a: can ignore all error reminders.

There is also a opterr variable if we set it to 0 (default is 1)

Getopts will ignore its own error only to show the system error

Note that the case 1 does not add a parameter value error two

./getopt.sh:option requires an argument-C
Invalid option:-

At this point, we add this to him.

[Email protected] mnt]#./getopt.sh-a
Invalid option:-
[Email protected] mnt]#./getopt.sh-b
Invalid option:-
[Email protected] mnt]#./getopt.sh-c
Invalid option:-
[Email protected] mnt]#./getopt.sh-d
This is-d, the ARG is!
[Email protected] mnt]#/getopt.sh-a 123
This is-a, the ARG is! 123

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Application of getopts in shell