Note: resetting ignore_case_always also resets ignore_case. Note Command-line arguments often take values. The GetOptions fun… If no linkage is explicitly specified and no ref HASH is passed, GetOptions Name "main::x" used only once: possible typo at ... Can't use string (...) as an HASH ref while "strict refs" in use at ... "my" variable masks earlier declaration in same scope, Can't call method ... on unblessed reference. Often we would like to give a default value to one of the options. don't have control over what the user supplies on the command line. In general, this means that options have long names instead of single letters, and are introduced with a double dash "--". Option names may be abbreviated to uniqueness, depending on configuration --trace --trace --trace --trace on the command line. ``--fpp-struct-return'' will set the variable $opt_fpp_struct_return. non-alphanumeric characters, it is taken to specify the option starter Supported option syntax includes: You can get rid of the undef warnings by making sure that the keys in %opts_hash are used like this: #default values for the options my %opts_hash = ( CbcDec => 0, CbcEnc => 0, CfbDec => 0, ); 0 many times it was supplied. The earliest development of newgetopt.pl started in 1990, with Perl version 4. The option name is always Command line options can be used to set values. If an ``@'' sign is appended to the argument specifier, the option is treated as an array. Although manipulating these variables still work, it is Each option specifier designates the name of the The same can be accomplish using an option with an optional value. at all. By default Getopt::Long also recognizes the short form of arguments, so this works too: $ ./license -h "David Farrell" David Farrell Type checking. We can run this script in various ways: The extra nice part is that because GetOptions allow the user to shorten the name of the options even this will work: Where we supplied --log instead of --logfile. Note: resetting bundling_override also resets bundling. This function retrieves and processes the command-line options with which your Perl program was invoked, based on the description of valid options that you provide. Default is 0. assigned ``value''. For example, With a command line of ``--size 24'' this will cause the variable For example: program --number=5 . Upon completion of Perl comes standard with two modules that assist programs in handling command line options: Getopt::Std and Getopt::Long. ``opt_''. always be empty upon succesful return of GetOptions since all options have Examples: but you can do a lot more with that module. If a REF CODE is supplied, the referenced subroutine is called with two The The option linkage is usually a reference to a variable that return false. equivalent to the example above: Linkage may be specified using either of the above methods, or both. The answer is that it depends on their order: It would be better to avoid such craziness, but of course, you, as the author of the script Let’s imagine I wanted to create a program for creating software licenses, like App::Software::License. We have already seen how to use Getopt::Long to process command line arguments, Using a starter argument is (For example in the DBI module we can set the Aside from GetOptions which has an extra behavior to support completion, all the other routines of GLC behave exactly the same as GL. provided ``vax'', ``v'', ``a'' and ``x'' have been defined to be valid If the user passes --verbose on the without turning on logging with --log does not have any meaning. If no linkage is explicitly specified and no ref HASH is passed, GetOptions will put the value in a global variable named after the option, prefixed by ``opt_''. to ``value'' (if the ``=value'' portion is omitted it defaults to 1). Other than that we just have two flags, usually true and the user can turn it off from the command line. The Getopt::Long module implements an extended function called GetOptions(). Each Option definition (one key value pair in the Hash) is composed of two elements, the key, referred to as option specification, and the value, referred to as option destination. which means the combination of -v, -a and -x. on the command line we'll get 0: which will probably simplify the code checking the value of $trace as won't have to create a special We can accomplish this in two ways: One of them is to have two separate one with a required =s string after it. Two Perl modules (Getopt and Getoptions::Long) work to extract program flags and arguments much like Getopt and Getopts do for shell programming. If you have any comments or questions, feel free to post them on the source of this page in GitHub. Getopt::Long::Complete (GLC) provides all the same exports as Getopt::Long (GL), for example "GetOptions" (exported by default), "GetOptionsFromArray", "Configure", etc. date: revision: tarball: summarized description: 2009.10.01: 0.53: Getopt-XML-0.53.tgz: Fixes issue that caused Make tests to fail, due to the test plan being configured for 8 … The pod for Getopt::Long is helpful, but I want a handy reference for some usages that I forget. Buy his eBooks or if you just would like to support him, do it via Patreon. Using a suitable default value, the program can find out whether $verbose is false by default, or disabled by using --noverbose. If parse ( ARGV , { key => value , # (1) option_specification => … Basically they are the same as the boolean arguments except the default is The user will run the program and it will print the software license text, with the license text customized for the user. arguments: one of the arguments is to turn logging on/off, and the other one is to supply specified in one of two ways: GetOptions is called with a list of option-descriptions, each of which $debug Enable debugging output. However one minor nit that Ive had up to now is that specifying the arguments and their destinations, along with defaults seemed a bit clumsy under strict. strongly deprecated. It can be some other change in the behavior of the script. will return false that will trigger the first die command showing the "Usage" string. The Perl modules, especially GetOptions::Long, are much more powerful and flexible. Options that start with ``--'' may have an argument appended, separated For array options, a reference to an array is used, e.g. In fact, the Perl 5 version of newgetopt.pl is just a wrapper around the module. Getopt::Long automatically exports the subroutine GetOptions. That is, we'll check if $verbose is trueand if it is, then we print something to the cons… That's when the or die added to this example, will be executed. This is for If configuration option getopt_compat is set (see section CONFIGURATION OPTIONS), options that start with ``+'' specified in the HASH. Linkage specified in the argument list takes precedence over the linkage overwritten. For example, the following call to Current working directory in Perl (cwd, pwd), Running external programs from Perl with system, qx or backticks - running external command and capturing the output, How to remove, copy or rename a file with Perl, Traversing the filesystem - using a queue, Installing a Perl Module from CPAN on Windows, Linux and Mac OSX, How to change @INC to find Perl modules in non-standard locations, How to replace a string in a file with Perl, Simple Database access using Perl DBI and SQL, Reading from LDAP in Perl using Net::LDAP, Global symbol requires explicit package name. This is long, explanatory help text which is displayed below the help containing the three columns of text: switch name, env value, default value. If explicit linkage is supplied, this must be a reference GetOptions: will accept a command line option ``size'' that must have an integer value. treated as a hash. Actually, in this case it might be better to start with 0 as the default value: my $trace = 0; ), Useless use of hash element in void context, Useless use of private variable in void context, Possible precedence issue with control flow operator, Have exceeded the maximum number of attempts (1000) to open temp file/dir. that this variable resides in the namespace of the calling program, not If a REF HASH is supplied, the option value should look like ``key'' or option specifier defines the name of the option and, optionally, the value For example, the UNIX "ps" command can be given the command li… with an ``='', e.g. The --machine option is expected to be followed by any string (which of course can be a number as well), We declare that by using :s at the end of the If a REF ARRAY is supplied, the new value is appended (pushed) to the will be set when the option is used. the same boolean argument. Also known as arguments with an optional value. Normally Getopt::Long does not care how many times the user supplies starter will be considered an option. just as the undef, but now, if we want, we can differentiate in the two cases when the user did not ask for Default values. configuring. Value(s) of the form ``name=value'' are set Both are optional, but if the user supplies either of those options, the user also has to supply For example: with command line ``-size 10 -sizes 24 -sizes 48'' will perform the I can see Getopt/Long.pm module is in the search path and it has the GetOptions subprogramme. Default is 1. Quick Hints for the Getopt::Long perl module. Its first argument will be $ARGV[0], second $ARGV, and so on. If the first argument to GetOptions is a string consisting of only Support for bundling of command line options, as was the case with the more traditional single-letter approach, is provided but not enabled by default. Caveat emptor. necessarily main. $ignorecase Ignore case when matching options. COMPATIBILITY Getopt::Long::GetOptions() is the successor of newgetopt.pl that came with Perl 4. --verbose, --quiet, or --debug that just by their mere presence make an impact. ``--foo=bar''. Note: resetting bundling also resets bundling_override. declarations mean. Getopt::Tabular is a Perl 5 module for table-driven argument parsing, vaguely inspired by John Ousterhout's Tk_ParseArgv. a file and we would like to allow the user to set the name of the logfile. Contact Gabor if you'd like to hire his service. array @opt_name. compatiblity with older implementations of the GNU ``getopt'' routine. Values for argument will put the value in a global variable named after the option, prefixed by If a REF SCALAR is supplied, the new value is stored in the referenced variable. $opt_ . Note: resetting ignore_case also resets ignore_case_always. takes a hash as an argument, in which the keys describe the data types and the values are references to variables that should be assigned the argument's value. With the new syntax --vax would be a single option, probably indicating a computer architecture. Whether non-options are allowed to be mixed with options. For example, we have a debugging mechanism If we provide the --verbose flag, it will be set to be 1, a true value. If an ``%'' sign is appended to the argument specifier, the option is The Getopt::Long module implements an extended getopt function called GetOptions(). strongly encouraged to use the new config routine. treated as an array. : with command line ``-sizes 24 -sizes 48'' will perform the equivalent of Find answers to Perl GetOptions: Undefined argument in option spec from the expert community at Experts Exchange variable. The following call is $verbose variable to 0. will do this for us. The only difference in the result is that if we set the default to be 0 then if we don't include any --trace Legacy. This is a special case of the boolean flags as in this case undef and 0 have These routines have in common that they use a single dash to identify option letters and they stop processing options when the first non-option is detected. Argument ... isn't numeric in numeric ... Can't locate object method "..." via package "1" (perhaps you forgot to load "1"? This function adheres to the POSIX syntax for command line options, with GNU extensions. at the end of the flag name where we define the flags and we just printed out The @ARGV array works same as a normal array. If a REF SCALAR is supplied, the new value is stored in the referenced Later in the code we'll see snippets like this: That is, we'll check if $verbose is true and if it is, then we print something to the console. If the user supplies either of those parameters without a proper value after it, the GetOptions function will print a warning and Perl GetOptions mandatory options. GetOptions, @ARGV will contain the rest (i.e. the syntax for variables are translated to underscores. reference to a hash is used, e.g. In this case, the element of the referenced hash with the key ``key'' is If the user passes --verbose on thecommand line, the variable $verbose will be set to some truevalue. The getopt module is the old-school command line option parser that supports the conventions established by the Unix function getopt().It parses an argument sequence, such as sys.argv and returns a sequence of (option, argument) pairs and a sequence of non-option arguments.. If in the definition of the parameter we only give the name ('verbose'), Getopt::Long will treat the option as a booleanflag. By default $verbose is undef and thus false. To allow specific option names, pass a list of option specifiers in the call to GetOptions() together with references to the variables in which you want the option values to be stored. If the option occurs more than once, the previous value is Getopt::Long provides basic type checking for strings, integers and floating point numbers. This is what the =s and the =i at the end of the We would like to enable a boolean flag such as--verbose, --quiet, or --debugthat just by their mere presence make an impact.Flags that don't need an additional value. the true name, not an abbreviation or alias. In boolean context this is still false Running the above code with different command line parameters look like this: We have the extra validation in case the user only supplies the --logfile FILENAME: If the user supplies --logfile without an argument the GetOptions will already warn about it and it result in: Example of using the <> option specifier: This will leave the non-options in @ARGV: Previous versions of Getopt::Long used variables for the purpose of The default is \*STDERR unless the exit value is less than 2 (in which case the default is \*STDOUT). the name of the file: In this case we had to add an extra validation to the code, to notify the user that providing --logfile FILENAME Alternatively, the first argument to GetOptions may be a reference to a referenced array. encountered. To yield a usable Perl variable, characters that are not part of Then again, we could have get the same effect by accepting an option called "trace" with a numerical value: In the next example we declare two options. flag. been processed, except when -- is used: will call the call-back routine for arg1 and arg2, and terminate leaving when mixing long options and bundles. arguments: the option name and the option value. We can do it by assigning this value to the $source_address variable before calling GetOptions. Let's see a couple of examples with various parameters: And two examples with improper invocation: I think it is much more simple for the user to supply --trace 4 that to write A lone dash - is considered an option, the corresponding Perl identifier is $opt_. Bundled options can also include a value in the bundle; this value has to with several levels of verbosity. Flags that don't need an additional value. For convenience, option specifiers may have a leading - or --, so it is possible to write: Also, assume specifiers ``foo=s'' and ``bar:s'' : In GNU or POSIX format, option names and values can be combined: With command line options ``-foo blech -bar 24 -ar xx -ar yy'' this will the assignment. If we run the script without providing the --verbose flag, the variable will remain undef. By default $verbose is undef and thus false. options. If I do perl ./script.pl -w --debug I get Name "main::result" used only once:possible typo at … ``+foo=bar''. This is the type of the command line switch, as defined by Getopt::Long. to an ARRAY. array, a reference to a hash or a reference to a subroutine. This can be very confusing, especially when permute is also set. allow the user to supply the --trace option multiple times and count how Since backward compatibility has always been extremely important, the current version of Getopt::Long still supports a lot of constructs that nowadays are no longer necessary or otherwise unwanted. it can take. $offset to get the value 24. Examples: type => '=s' type => '=s@', verbose => 'Some long help text' This key, value pair is optional. For example, at the time we declare it using my. consists of two elements: the option specifier and the option linkage. You can inspect $Getopt::Long::major_version and A lone dash - is considered an option, the corresponding Perl identifier is arg2 in @ARGV. option name as in logfile:s. In this case we don't need the extra parameter checking, though the actual code is quite similar to what we have earlier. characters. will perform the equivalent of the assignment. Let’s start with the license holder’s name: I start by importing Getopt::Long, it’s part of the core Perl distribution, so if you have Perl installed, you should already have it. by setting the element of the hash %opt_name with key ``name'' -input A reference to a filehandle, or the pathname of a file from which the invoking script's pod documentation should be read. If in the definition of the parameter we only give the name ('verbose'), Getopt::Long will treat the option as a boolean different meaning: We put an exclamation mark ! So far nothing changed. a boolean argument, it only cares if it was supplied at least once, or not An incremental option is specified with a plus + after the option name: my $verbose = ''; # option variable with default value (false) GetOptions ('verbose+' => \$verbose); verboseness, and when the user explicitly ask for no verboseness: In certain situation this might be useful, though I have to admit, I have not encountered any such situation yet. If a non-option call-back routine is specified, @ARGV will See also permute, which is the opposite of require_order. Note: Using option bundling can easily lead to unexpected results, especially The linkage specifier can be a reference to a scalar, a reference to an array, a reference to a hash or a reference to a subroutine. As a result, its development, and the development of Getopt::Long, has gone through several stages. One way to accomplish this is to To do this, the program will need to process a few arguments from the user - a perfect use case for Getopt::Long! It is fully upward compatible. be the last part of the bundle, e.g. equivalent of the assignments. # -input handle A reference to a filehandle, or the pathname of a file from which the invoking script's pod documentation should be read. Everything starting with one of these characters from the or ``-'' may also include their arguments, e.g. For example in the case of the --from field we might want it to default to the word 'Maven'. the --verbose and the --noverbose flags to the script. How to pass both mandatory and optional command line arguments , That variable doesn't need a default value since it is mandatory, and it Processing of named options by GetOptions is the same as above. If require_order is set, options processing terminates when the first non-option is check to make sure $trace is defined. Minimal requirement to build a sane CPAN package, Statement modifiers: reversed if statements, Formatted printing in Perl using printf and sprintf, how to use Getopt::Long to process command line arguments. a value. specifiers are: A double dash on itself -- signals end of the options list. If no logfilename was given, our script will print its log to STDERR. For example in one script I have an --all flag which means, the script needs to process all the files in the the given directory. The Hash-bang line, or how to make a Perl scripts executable on Linux, Core Perl documentation and CPAN module documentation, Common Warnings and Error messages in Perl, Prompt, read from STDIN, read from the keyboard in Perl, Automatic string to number conversion or casting in Perl, Conditional statements, using if, else, elsif in Perl, String operators: concatenation (. Value(s) are not set, but pushed into ``key=value'' (if the ``=value'' is omitted then a value of 1 is implied). DESCRIPTION. For hash options (an option whose argument looks like ``name=value''), a For example we would like to allow the user to turn on/off logging to If an ``@'' sign is appended to the argument specifier, the option is The + sign at the end of the definition HASH describing the linkage for the options. Getopt::Long is a valuable perl module that provides functionality for processing command line options. option auto_abbrev. explicit linkage is supplied, this must be a reference to a HASH. the value of $verbose. the equivalent of the assignment. The default is \ *STDERR unless the exit value is less than 2 (in which case the default is \ *STDOUT). Getopt::Long exports a function, GetOptions(), which processes @ARGV to do something useful with these arguments, such as set variables or run blocks of code. $Getopt::Long::minor_version for the individual components. command line, the variable $verbose will be set to some true value. Getopt::Long is a basic part of the Perl toolset. What are -e, -z, -s, -M, -A, -C, -r, -w, -x, -o, -f, -d , -l in Perl? : with command line ``--define foo=hello --define bar=world'' will perform Besides, it is much easier. The linkage specifier can be a reference to a scalar, a reference to an Let's see how else can we use the Getopt::Long module: We would like to enable a boolean flag such as Default is $REQUIRE_ORDER if environment variable POSIXLY_CORRECT has been set, $PERMUTE otherwise. The command line options are taken from array @ARGV. require 'ruby-getoptions' options , remaining = GetOptions . TraceLevel to any number between 0-15). option, optionally followed by an argument specifier. the non-options) To yield a usable Perl variable, characters that are not part of the syntax for variables are translated to underscores. of the command line. These values can be Gabor can help refactor your old Perl code-base. Module Getopt::Std provides two subroutines, getopt and getopts . There are cases when we would like to add meaning to the duplication of The difference is that now we can supply a --noverbose flag that will set the the --trace option is expected to be followed by an integer. ), repetition (x), undef, the initial value and the defined function of Perl, Strings in Perl: quoted, interpolated and escaped, Here documents, or how to create multi-line strings in Perl, String functions: length, lc, uc, index, substr, Standard output, standard error and command line redirection, seek - move the position in the filehandle in Perl, Processing command line arguments - @ARGV in Perl, How to process command line arguments in Perl using Getopt::Long, Advanced usage of Getopt::Long for accepting command line arguments, Perl split - to cut up a string into pieces, Scalar and List context in Perl, the size of an array, Reading from a file in scalar and list context, Manipulating Perl arrays: shift, unshift, push, pop, Reverse Polish Calculator in Perl using a stack, Loop controls: next, last, continue, break, Passing multiple parameters to a function in Perl, Variable number of parameters in Perl subroutines, Returning multiple values or a list from a subroutine in Perl, Understanding recursive subroutines - traversing a directory tree, Count the frequency of words in text using Perl, trim - removing leading and trailing white spaces with Perl. Of course it does not have to be some extra printing. Just for the curiosity, after reading the next part I came back and wanted to see what happens if we supply both Is that now we can supply a value in the hash following call to GetOptions: provides!, e.g especially GetOptions::Long module implements an extended function called (. Optionally followed by an argument specifier, the first argument will be considered option... Call to GetOptions may be a reference to a variable that will be to! Are much more powerful and flexible, @ ARGV array works same as result. Means the combination of -v, -a and -x levels of verbosity in 1990, Perl!, probably indicating a computer architecture 1, a reference to an.. Option linkage is supplied, the following call to GetOptions may be a reference a! Debugging mechanism with several levels of verbosity the search path and it the! Specifier defines the name of the assignments SCALAR is supplied, the following call is equivalent the., options processing terminates when the option linkage is supplied, the argument! Of verbosity of `` -- fpp-struct-return '' will perform the equivalent of the assignment a -- noverbose flag will. Stored in the DBI module we can supply a value, its,. More powerful and flexible both are optional, but pushed into array @.. Is helpful, but I want a handy reference for some usages that forget! Verbose variable to 0 supply a value dash - is considered an option, optionally, the Perl 5 of... With command line `` -sizes 24 -sizes 48 '' will perform the of. Confusing, especially when permute is also set feel free to post them on the source of this page GitHub! Whether non-options are allowed to be mixed with options each option specifier defines the name of the.... For compatiblity with older implementations of the assignment if explicit linkage is supplied, the new is... Bar=World '' will set the variable $ offset to get the value of verbose! First non-option is perl getoptions default value started in 1990, with GNU extensions 5 version newgetopt.pl. Example, the option is treated as an array is used,.. Getopt/Long.Pm module is in the bundle, e.g -size 10 -sizes 24 -sizes 48 '' will perform the of... Is equivalent to the argument list takes precedence over the linkage for the:... Value is stored in the referenced variable be accomplish using an option lone -... The assignments 1, a reference to a variable that will set variable. Posixly_Correct has been set, but I want a handy reference for some usages that forget! Are taken from array @ opt_name also set v '', `` a '' and x... Getoptions ( ) undef and thus false permute is also set =s and the =i at the time we it. If an `` @ '' sign is appended ( pushed ) to the example above: may... The syntax for variables are translated to underscores be valid options be mixed with options if the user will the... '' that must have an argument appended, separated with an optional.. Permute otherwise be valid options the individual components assigning this value to one of these characters the... Extended Getopt function called GetOptions ( ) it can take integers and floating point numbers support completion, the! Argv, and so on single option, optionally, the referenced variable the duplication of the same GL! License text customized for the user passes -- verbose flag, it strongly! Only non-alphanumeric characters, it is taken to specify the option, the new config routine signals end the! That must have an argument specifier, the referenced array very confusing, especially when permute is also set with. Variable resides in the argument specifier, the variable $ verbose will be set to some truevalue GetOptions.! You 'd like to hire his service flag name where we define flags! An abbreviation or alias a program for creating software licenses, like App:Software... Second $ ARGV, and the development of newgetopt.pl is just a around! Die added to this example, at the end of the assignment my... Linkage for the user also has to be some extra printing as defined by Getopt::Std two. Call is equivalent to the argument list takes precedence over the linkage for user! -Sizes 24 -sizes 48 '' will set the TraceLevel to any number between 0-15 ) variable... Add meaning to the argument specifier, the variable $ verbose is undef and false... Has the GetOptions subprogramme basic part of the flag name where we define the flags and we just out... Only non-alphanumeric characters, it will be considered an option whose argument like! Assigned `` value '' is always the true name, not necessarily main verbose is and... It via Patreon usages that I forget it will be set when the first argument will be.. Variable will remain undef when the first argument to GetOptions is a Perl 5 version of is. That I forget program, not an abbreviation or alias added to this,! -- noverbose flag that will set the variable $ opt_fpp_struct_return free to post them on the command line,. $ ARGV, and so on can do it by assigning this value has to supply a -- flag! Sign at the end of the declarations mean are taken from array @ opt_name to some perl getoptions default value the specifier..., one with a command line `` -sizes 24 -sizes 48 '' will perform the equivalent of the.! Which has an extra behavior to support completion, all the other routines GLC. License text, with the license text customized for the user also has to supply a in! @ opt_name can set the TraceLevel to any number between 0-15 ) ( pushed ) to the duplication of flag. Although manipulating these variables still work, it is taken to specify the option, following! 'Maven ' this can be very confusing, especially when permute is also set them... Option is used floating point numbers provides functionality for processing command line, user! You can perl getoptions default value $ Getopt::Std provides two subroutines, Getopt and getopts GitHub., depending on configuration option auto_abbrev that 's when the first non-option is encountered the will. The same boolean argument it to default to the referenced variable licenses, like App:Software... Easily lead to unexpected results perl getoptions default value especially GetOptions: will accept a line... An extended Getopt function called GetOptions ( ) more than once, the variable will remain undef the. Are allowed to be valid options add meaning to the word 'Maven ' its development, and the option.. The pod for Getopt::Long module implements an extended function called GetOptions (.. If no logfilename was given, our script will print its log to STDERR '' sign is appended ( ). Is also set will be set to some true value computer architecture to a! This is what the =s and the option name and the =i at the of! Be mixed with options a valuable Perl module that provides functionality for processing command line options, the! May be a reference to an array: the option name and the development Getopt... Getoptions subprogramme let ’ s imagine I wanted to create a program for software... Posix syntax for variables are translated to underscores assigned `` value '' and! Of require_order been set, but if the option, the option and,,. For argument specifiers are: a double dash on itself -- signals of. Above methods, or both, and the development of Getopt::Long module implements an extended called! The behavior of the above methods, or both are translated to underscores the following call is equivalent the! And $ Getopt::Long module implements an extended function called GetOptions ( ) linkage! Over the linkage for the user will run the program and it will set! Variable before calling GetOptions that we just printed out the value of $ verbose mixing long options and.! Is a string perl getoptions default value of only non-alphanumeric characters, it is strongly to. Post them on the command line options are taken from array @.. Value to one of the bundle, e.g the difference is that now we can supply a value the... -- vax would be a reference to a variable that will set the TraceLevel to any number between ). To this example, will be $ ARGV [ 0 perl getoptions default value, second $ ARGV [ ]... New config routine argument parsing, vaguely inspired by John Ousterhout 's Tk_ParseArgv rest! Especially GetOptions::Long is helpful, but if the user passes -- verbose on the source this! Version 4 key `` key '' is assigned `` value '' a double dash itself! Was given, our script will print its log to STDERR GetOptions is a 5! Default is $ require_order if environment variable POSIXLY_CORRECT has been set, $ permute otherwise option.... Argument looks like `` name=value '' ), a true value a REF SCALAR supplied! Looks like `` name=value '' ), a reference to a filehandle, or.! We might want it to default to the $ source_address variable before calling.! Integer value the POSIX syntax for variables are translated to underscores implementations of script... To some true value or the pathname of a file from which the invoking script 's documentation!