getopts - parse utility options
getopts optstring name [arg...]
The getopts utility can be used to retrieve options and option-arguments from a list of parameters. It supports the utility argument syntax guidelines 3 to 10, inclusive, described in the XBD specification, Utility Syntax Guidelines .
Each time it is invoked, the getopts utility 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 will be initialised to 1.
When the option requires an option-argument, the getopts utility will 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 will 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 will be set to the question-mark (?) character. In this case, if the first character in optstring is a colon (:), the shell variable OPTARG will be set to the option character found, but no output will be written to standard error; otherwise, the shell variable OPTARG will be unset and a diagnostic message will be 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 will be set to the colon character and the shell variable OPTARG will be set to the option character found.
- Otherwise, the shell variable specified by name will be set to the question-mark character, the shell variable OPTARG will be unset, and a diagnostic message will be 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; a diagnostic message will be written as stated, but the exit status will be zero.
When the end of options is encountered, the getopts utility will exit with a return value greater than zero; the shell variable OPTIND will be set to the index of the first non-option-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 non-option-arguments; the name variable will be 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; see
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.
The following operands are supported:
- A string containing the option characters recognised 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. (See also the XSH specification getopt() function.) 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.
- The name of a shell variable that will be set by the getopts utility to the option character that was found.
The getopts utility by default will parse positional parameters passed to the invoking shell procedure. If args are given, they will be parsed instead of the positional parameters.
The following environment variables affect the execution of getopts:
- Provide a default value for the internationalisation variables that are unset or null. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined.
- If set to a non-empty string value, override the values of all the other internationalisation variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single- as opposed to multi-byte characters in arguments and input files).
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- Determine the location of message catalogues for the processing of LC_MESSAGES .
- This variable will be used by the getopts utility as the index of the next argument to be processed.
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 (see
Special Parameters) at the time the getopts utility is invoked. A name equivalent to: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.
The following exit values are returned:
- An option, specified or unspecified by optstring, was found.
- The end of options was encountered or an error occurred.
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:it will not affect the shell variables in the caller's environment.
(getopts abc value "$@") nohup getopts ... find . -exec getopts ... \;
Note that shell functions share OPTIND with the calling shell even though the positional parameters are changed. Functions that want to use getopts to parse their arguments will usually want to save the value of OPTIND on entry and restore it before returning. However, there will be cases when a function will want to 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" "$*"
The XSH specification description of getopt().