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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GETOPTS(1P) POSIX Programmer's Manual GETOPTS(1P)
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.
getopts — parse utility options
getopts optstring name [arg...]
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.
None.
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.
Not used.
None.
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.
Default.
Not used.
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 "$0"
may be used.
* If an option is found that was not specified in optstring,
this error is identified and the invalid option character
shall be identified in the message.
* If an option requiring an option-argument is found, but an
option-argument is not found, this error shall be identified
and the invalid option character shall be identified in the
message.
None.
None.
The following exit values shall be returned:
0 An option, specified or unspecified by optstring, was found.
>0 The end of options was encountered or an error occurred.
Default.
The following sections are informative.
Since getopts affects the current shell execution environment, it
is generally provided as a shell regular built-in. If it is called
in a subshell or separate utility execution environment, such as
one of the following:
(getopts abc value "$@")
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.
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$*"
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.
None.
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(3p)
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(1P)
Pages that refer to this page: pax(1p), getopt(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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