NAME

getopts — parse utility options

SYNOPSIS

getopts optstring name [param...]

DESCRIPTION

The getopts utility shall retrieve options and option-arguments from a list of parameters. It shall support the Utility Syntax Guidelines 3 to 10, inclusive, described in XBD 12.2 Utility Syntax Guidelines.

When the shell is first invoked, the shell variable OPTIND shall be initialized to 1. Each time getopts is invoked, it shall place the value of the next option found in the parameter list in the shell variable specified by the name operand and the shell variable OPTIND shall be set as follows:

• When getopts successfully parses an option that takes an option-argument (that is, a character followed by <colon> in optstring, and exit status is 0), the value of OPTIND shall be the integer index of the next element of the parameter list (if any; see OPERANDS below) to be searched for an option character. Index 1 identifies the first element of the parameter list.

• When getopts reports end of options (that is, when exit status is 1), the value of OPTIND shall be the integer index of the next element of the parameter list (if any).

• In all other cases, the value of OPTIND is unspecified, but shall encode the information needed for the next invocation of getopts to resume parsing options after the option just parsed.

When the option requires an option-argument, the getopts utility shall place 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 shall be 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 shall be set to the <question-mark> ('?') character. In this case, if the first character in optstring is a <colon> (':'), the shell variable OPTARG shall be set to the option character found, but no output shall be written to standard error; otherwise, 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 processing.

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 character 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 processing; a diagnostic message shall be written as stated, but the exit status shall be zero.

When the end of options is encountered, the getopts utility shall exit with a return value of one; the shell variable OPTIND shall be set to the index of the argument containing the first operand in the parameter list, or the value 1 plus the number of elements in the parameter list if there are no operands in the parameter list; the name variable shall be set to the <question-mark> character. Any of the following shall identify the end of options: the first "--" element of the parameter list that is not an option-argument, finding an element of the parameter list that is not an option-argument and does not begin with a '-', or encountering an error.

The shell variables OPTIND and OPTARG shall not be exported by default. An error in setting any of these variables (such as if name has previously been marked readonly) shall be considered an error of getopts processing, and shall result in a return value greater than one.

The getopts utility can affect OPTIND , OPTARG , and the shell variable specified by the name operand, within the current shell execution environment; see 2.13 Shell Execution Environment.

If the application sets OPTIND to the value 1, a new set of parameters can be used: either the current positional parameters or new param values. Any other attempt to invoke getopts multiple times in a single shell execution environment with parameters (positional parameters or param operands) that are not the same in all invocations, or with an OPTIND value modified by the application to be a value other than 1, produces unspecified results.

OPTIONS

None.

OPERANDS

The following operands shall be supported:

optstring

A string containing the option characters recognized by the utility invoking getopts. If a character is followed by a <colon>, the option shall 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 shall 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 recognized if it is not supplied as a separate argument when getopts is invoked. (See also the getopt() function defined in the System Interfaces volume of POSIX.1-2024.) The characters <question-mark> and <colon> shall not be used as option characters by an application. The use of other option characters that are not alphanumeric produces unspecified results. Whether or not the option-argument is supplied as a separate argument from the option character, the value in OPTARG shall only be the characters of the option-argument. The first character in optstring determines how getopts behaves if an option character is not known or an option-argument is missing.

name

The name of a shell variable that shall be set by the getopts utility to the option character that was found.

By default, the list of parameters parsed by the getopts utility shall be the positional parameters currently set in the invoking shell environment ("$@"). If param operands are given, they shall be parsed instead of the positional parameters. Note that the next element of the parameter list need not exist; in this case, OPTIND will be set to $#+1 or the number of param operands plus 1.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of getopts:

LANG

Provide a default value for the internationalization variables that are unset or null. (See XBD 8.2 Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.

NLSPATH

^[XSI] Determine the location of messages objects and message catalogs.

OPTIND

This variable shall be used by the getopts utility as the index of the next argument to be processed.

ASYNCHRONOUS EVENTS

Default.

STDOUT

Not used.

STDERR

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

• The invoking program name shall be identified in the message. The invoking program name shall be the value of the shell special parameter 0 (see 2.5.2 Special Parameters) 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 is identified and the invalid option character shall be identified in the message.

• If an option requiring an option-argument is found, but an option-argument is not found, this error shall be identified and the invalid option character shall be identified in the message.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

 0

An option, specified or unspecified by optstring, was found.

 1

The end of options was encountered.

>1

An error occurred.

CONSEQUENCES OF ERRORS

Default.

APPLICATION USAGE

This utility is required to be intrinsic. See 1.7 Intrinsic Utilities for details.

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. If the calling shell and any of its functions uses getopts to parse arguments, the results are unspecified.

EXAMPLES

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" $0
          exit 2;;
    esac
done
if [ -n "$aflag" ]; then
    printf "Option -a specified\n"
fi
if [ -n "$bflag" ]; then
    printf 'Option -b "%s" specified\n' "$bval"
fi
shift $(($OPTIND - 1))
printf "Remaining arguments are: %s\n" "$*"

RATIONALE

The getopts utility was chosen in preference to the System V getopt utility because getopts handles option-arguments containing <blank> characters.

The OPTARG variable is not mentioned in the ENVIRONMENT VARIABLES section because it does not affect the execution of getopts; it is one of the few "output-only" variables used by the standard utilities.

The <colon> is not allowed as an option character because that is not historical behavior, and it violates the Utility Syntax Guidelines. The <colon> is now specified to behave as in the KornShell version of the getopts utility; when used as the first character in the optstring operand, it disables diagnostics concerning missing option-arguments and unexpected option characters. This replaces the use of the OPTERR variable that was specified in an early proposal.

Although a leading <plus-sign> in optstring is required to have no effect on the behavior of getopt(), this standard intentionally allows implementations of the getopts utility to use a leading <plus-sign> as an extension that alters behavior. In fact, a <plus-sign> anywhere in the optstring in the getopts utility produces unspecified behavior.

The formats of the diagnostic messages produced by the getopts utility and the getopt() function are not fully specified because implementations with superior ("friendlier") formats objected to the formats used by some historical implementations. The standard developers considered it important that the information in the messages used be uniform between getopts and getopt(). Exact duplication of the messages might not be possible, particularly if a utility is built on another system that has a different getopt() function, but the messages must have specific information included so that the program name, invalid option character, and type of error can be distinguished by a user.

Only a rare application program intercepts a getopts standard error message and wants to parse it. Therefore, implementations are free to choose the most usable messages they can devise. The following formats are used by many historical implementations:

"%s: illegal option -- %c\n", <program name>, <option character>


"%s: option requires an argument -- %c\n", <program name>, \
    <option character>

Historical shells with built-in versions of getopt() or getopts have used different formats, frequently not even indicating the option character found in error.

FUTURE DIRECTIONS

None.

SEE ALSO

2.5.2 Special Parameters

XBD 8. Environment Variables, 12.2 Utility Syntax Guidelines

XSH getopt

CHANGE HISTORY

First released in Issue 4.

Issue 6

The normative text is reworded to avoid use of the term "must" for application requirements.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XCU/TC1-2008/0092 [159] is applied.

Issue 8

Austin Group Defect 191 is applied, adding a paragraph about leading <plus-sign> to the RATIONALE section.

Austin Group Defect 367 is applied, requiring that getopts distinguishes between encountering the end of options and an error occurring, setting its exit status to one and greater than one, respectively.

Austin Group Defect 854 is applied, adding a note to the APPLICATION USAGE section that this utility is required to be intrinsic.

Austin Group Defect 1122 is applied, changing the description of NLSPATH .

Austin Group Defect 1442 is applied, changing the EXAMPLES section.

Austin Group Defect 1784 is applied, clarifying several aspects of getopts behavior and changing the value of OPTIND to be unspecified in some circumstances.