getopts(1)

NAME

getopts — parse utility (command) options

SYNOPSIS

getopts optstring name [arg ...]

DESCRIPTION

getopts is used to retrieve options and option-arguments from a list of parameters.

Each time it is invoked, getopts places the value of the next option in the shell variable specified by the name operand 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 the option requires an option-argument, getopts places it in the shell variable OPTARG. If no option was found, or if the option that was found does not have an option-argument, OPTARG is unset.

If an option character not contained in the optstring operand is found where an option character is expected, the shell variable specified by name is set to the question-mark (?) character. In this case, if the first character in optstring is a colon (:), the shell variable OPTARG is set to the option character found, but no output is written to standard error; otherwise, the shell variable OPTARG is unset and a diagnostic message is 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 getopts processing.

If an option-argument is missing:

If the first character of optstring is a colon, the shell variable specified by name is set to the colon character and the shell variable OPTARG is set to the option character found.
Otherwise, the shell variable specified by name is set to the question-mark character, the shell variable OPTARG is unset, and a diagnostic message is written to the standard error. This condition is considered to be an error detected in the way arguments are presented to the invoking application, but is not an error in getopts processing; a diagnostic message is written as stated, but the exit status is zero.

When the end of options is encountered, getopts exits with a return value greater than zero. The shell variable OPTIND is set to the index of the first nonoption-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 nonoption-arguments; the name variable is set to the question-mark character. Any of the following identifies the end of options: the special option --, finding an argument that does not begin with a -, or encountering an error.

The shell variables OPTIND and OPTARG are local to the caller of getopts and are not exported by default.

The shell variable specified by the name operand, OPTIND, and OPTARG affect the current shell execution environment.

Operands

The following operands are supported:

optstring: A string containing the option characters recognized by the utility invoking getopts. If a character is followed by a colon (:), the option will be expected to have an argument, which should be supplied as a separate argument. Applications should specify an option character and its option-argument as separate arguments, but getopts will interpret the characters following an option character requiring arguments as an argument whether or not this is done. An explicit null option-argument need not be recognised if it is not supplied as a separate argument when getopts is invoked. The characters question-mark (?) and colon (:) must not be used as option characters by an application. The use of other option characters that are not alphanumeric produces unspecified results. If the option-argument is not supplied as a separate argument from the option character, the value in OPTARG will be stripped of the option character and the -. The first character in optstring will determine how getopts will behave if an option character is not known or an option-argument is missing.
name: The name of a shell variable that is set by getopts to the option character that was found.

getopts by default parses positional parameters passed to the invoking shell procedures. If args are given, they are parsed instead of the positional parameters.

EXTERNAL INFLUENCES

Environment Variable

The following environment variable affects the execution of the getopts utility:

OPTIND: Used by getopts as the index of the next argument to be processed.

ERRORS

Whenever an error is detected and the first character in the optstring operand is not a colon (:), a diagnostic message will be written to standard error with the following information in an unspecified format:

The invoking program name will be identified in the message. The invoking program name will be the value of the shell special parameter 0 at the time the getopts utility is invoked. A name equivalent to:
basename "$0"
may be used.
If an option is found that was not specified in optstring, this error will be identified and the invalid option character will be identified in the message.
If an option requiring an option-argument is found, but an option-argument is not found, this error will be identified and the invalid option character will be identified in the message.

EXAMPLES

Since getopts affects the current shell execution environment, it is generally provided as a shell regular built-in. If it is called in a subshell or separate utility execution environment such as one of the following:

(getopts abc value "$@") 
nohup getopts ... 
find -exec getopts ...\; 

it does not affect the shell variables in the caller's environment.

Note that shell functions share OPTIND with the calling shell even though the positional parameters are changed. Functions that use getopts to parse their arguments should save the value of OPTIND on entry and restore it before returning. However, there will be cases when a function must change OPTIND for the calling shell.

The following example script parses and displays its 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" "$*"

STANDARDS CONFORMANCE

getopts: XPG4, POSIX.2