getopts Command

Purpose

Processes command-line arguments and checks for valid options.

Syntax

getopts OptionString Name [ Argument ...]

Description

The getopts command is a Korn/POSIX Shell built-in command that retrieves options and option-arguments from a list of parameters. An option begins with a + (plus sign) or a - (minus sign) followed by a character. An option that does not begin with either a + or a - ends the OptionString. Each time the getopts command is invoked, it places the value of the next option in Name and the index of the next argument to be processed in the shell variable OPTIND. Whenever the shell is invoked, OPTIND is initialized to 1. When an option begins with +, a + is prepended to the value in Name.

If a character in OptionString is followed by a : (colon), that option is expected to have an argument. When an option requires an option-argument, the getopts command places it in the variable OPTARG.

When an option character not contained in OptionString is found, or an option found does not have the required option-argument:

If OptionString does not begin with a : (colon),
- Name will be set to a ? (question mark) character,
- OPTARG. will be unset, and
- a diagnostic message will be written to standard error.

This condition is considered to be an error detected in the way arguments were presented to the invoking application, but is not an error in the processing of the getopts command; a diagnostic message will be written as stated, but the exit status will be zero.

If OptionString begins with a : (colon),
- Name will be set to a ? (question mark) character for an unknown option or to a : (colon) character for a missing required option,
- OPTARG will be set to the option character found, and
- no output will be written to standard error.

Any of the following identifies the end of options: the special option - -, finding an argument that does not begin with a -, or +, or encountering an error.

When the end of options is encountered:

the getopts command will exit with a return value greater than zero,
OPTARG will be set to the index of the first non-option-argument, where the first - - argument is considered to be an option-argument if there are no other non-option-arguments appearing before it, or the value $#+1 if there are no non-option-arguments,
Name will be set to a ? (question mark) character.

Parameters

Item	Description
OptionString	Contains the string of option characters recognized by the getopts command. If a character is followed by a colon, that option is expected to have an argument, which should be supplied as a separate argument. The options can be separated from the argument by blanks. The first character in OptionString determines how the getopts command behaves if an option character is not known or an option-argument is missing. Note: The characters question mark and colon must not be used as option characters by an application. The use of other characters that are not alphanumeric produces unspecified results.
Name	Set by the getopts command to the option character that was found.
Argument ...	One or more strings separated by white space, checked by the getopts command for legal options. If Argument is omitted, the positional parameters are used. Note: Generally, you won't specify Argument as part of the getopts command, but it may be helpful when debugging your script.

Item

Description

OptionString

Contains the string of option characters recognized by the getopts command. If a character is followed by a colon, that option is expected to have an argument, which should be supplied as a separate argument. The options can be separated from the argument by blanks. The first character in OptionString determines how the getopts command behaves if an option character is not known or an option-argument is missing.

Note: The characters question mark and colon must not be used as option characters by an application. The use of other characters that are not alphanumeric produces unspecified results.

Name

Set by the getopts command to the option character that was found.

Argument ...

One or more strings separated by white space, checked by the getopts command for legal options. If Argument is omitted, the positional parameters are used.

Note: Generally, you won't specify Argument as part of the getopts command, but it may be helpful when debugging your script.

Exit Status

This command returns the following exit values:

Item	Description
0	An option, specified or unspecified by OptionString, was found.
>0	The end of options was encountered or an error occurred.

Examples

The following getopts command specifies that a, b, and c are valid options, and that options a and c have arguments:
```
getopts a:bc: OPT
```
The following getopts command specifies that a, b, and c are valid options, that options a and b have arguments, and that getopts set the value of OPT to ? when it encounters an undefined option on the command line:
```
getopts :a:b:c OPT
```

The following script parses and displays it arguments:

aflag=
bflag=
 
while getopts ab: name
do
            case $name in
            a)     aflag=1;;
            b)     bflag=1
                          bval="$OPTARG";;
            ?)     printf "Usage: %s: [-a] [-b value] args\n" $0
                          exit 2;;
           esac
done
 
if [ ! -z "$aflag" ]; then
           printf "Option -a specified\n"
fi
 
if [ ! -z "$bflag" ]; then
           printf 'Option -b "%s" specified\n' "$bval"
fi
 
shift $(($OPTIND -1))
printf "Remaining arguments are: %s\n" "$*"