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NAME
getopts — parse utility options
SYNOPSIS
getopts optstring name [arg...]
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 the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
Each time it is invoked, the getopts utility shall place 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 shall be initialized to 1.
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 greater than
zero; the shell variable OPTIND shall be set to the index of the first operand, or the value "$#"+1 if
there are no operands; the name variable shall be set to the <question-mark> character. Any of the
following shall identify the end of options: the first "--" argument that is not an option-argument,
finding an argument that is not an option-argument and does not begin with a '-', or encountering an
error.
The shell variables OPTIND and OPTARG shall be local to the caller of getopts and shall not be exported
by default.
The shell variable specified by the name operand, OPTIND, and OPTARG shall affect the current shell
execution environment; see Section 2.12, 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 arg values. Any other attempt to invoke getopts multiple times in a single
shell execution environment with parameters (positional parameters or arg operands) that are not the same
in all invocations, or with an OPTIND value modified 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.1‐2017.) 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. If the option-argument is not supplied as a separate argument
from the option character, the value in OPTARG shall be stripped of the option character and
the '-'. 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.
The getopts utility by default shall parse positional parameters passed to the invoking shell procedure.
If args are given, they shall be parsed instead of the positional parameters.
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 the
Base Definitions volume of POSIX.1‐2017, Section 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 Determine the location of message catalogs for the processing of LC_MESSAGES.
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 Section 2.5.2, Special Parameters) at the time the
getopts utility is invoked. A name equivalent to:
basename "$0"
may be used.
* If an option is found that was not specified in optstring, this error is identified and the invalid
option character shall be identified in the message.
* If an option requiring an option-argument is found, but an option-argument is not found, this error
shall be identified and the invalid option character shall be identified in the message.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 An option, specified or unspecified by optstring, was found.
>0 The end of options was encountered or an error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
Since getopts affects the current shell execution environment, it is generally provided as a shell
regular built-in. If it is called in a subshell or separate utility execution environment, such as one of
the following:
(getopts abc value "$@")
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" $0
exit 2;;
esac
done
if [ ! -z "$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$*"
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.
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
Section 2.5.2, Special Parameters
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility
Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, getopt()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 GETOPTS(1POSIX)