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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
this interface may differ (consult the corresponding Linux manual page for details of
Linux behavior), or the interface may not be implemented on Linux.
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 .