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Exporter(3perl)                   Perl Programmers Reference Guide                   Exporter(3perl)

NAME
       Exporter - Implements default import method for modules

SYNOPSIS
       In module YourModule.pm:

         package YourModule;
         use Exporter 'import';
         our @EXPORT_OK = qw(munge frobnicate);  # symbols to export on request

       or

         package YourModule;
         require Exporter;
         our @ISA = qw(Exporter);  # inherit all of Exporter's methods
         our @EXPORT_OK = qw(munge frobnicate);  # symbols to export on request

       or

         package YourModule;
         use parent 'Exporter';  # inherit all of Exporter's methods
         our @EXPORT_OK = qw(munge frobnicate);  # symbols to export on request

       In other files which wish to use "YourModule":

         use YourModule qw(frobnicate);      # import listed symbols
         frobnicate ($left, $right)          # calls YourModule::frobnicate

       Take a look at "Good Practices" for some variants you will like to use in modern Perl code.

DESCRIPTION
       The Exporter module implements an "import" method which allows a module to export functions
       and variables to its users' namespaces.  Many modules use Exporter rather than implementing
       their own "import" method because Exporter provides a highly flexible interface, with an
       implementation optimised for the common case.

       Perl automatically calls the "import" method when processing a "use" statement for a module.
       Modules and "use" are documented in perlfunc and perlmod.  Understanding the concept of
       modules and how the "use" statement operates is important to understanding the Exporter.

   How to Export
       The arrays @EXPORT and @EXPORT_OK in a module hold lists of symbols that are going to be
       exported into the users name space by default, or which they can request to be exported,
       respectively.  The symbols can represent functions, scalars, arrays, hashes, or typeglobs.
       The symbols must be given by full name with the exception that the ampersand in front of a
       function is optional, e.g.

         our @EXPORT    = qw(afunc $scalar @array);   # afunc is a function
         our @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc

       If you are only exporting function names it is recommended to omit the ampersand, as the
       implementation is faster this way.

   Selecting What to Export
       Do not export method names!

       Do not export anything else by default without a good reason!

       Exports pollute the namespace of the module user.  If you must export try to use @EXPORT_OK
       in preference to @EXPORT and avoid short or common symbol names to reduce the risk of name
       clashes.

       Generally anything not exported is still accessible from outside the module using the
       "YourModule::item_name" (or "$blessed_ref->method") syntax.  By convention you can use a
       leading underscore on names to informally indicate that they are 'internal' and not for
       public use.

       (It is actually possible to get private functions by saying:

         my $subref = sub { ... };
         $subref->(@args);            # Call it as a function
         $obj->$subref(@args);        # Use it as a method

       However if you use them for methods it is up to you to figure out how to make inheritance
       work.)

       As a general rule, if the module is trying to be object oriented then export nothing.  If
       it's just a collection of functions then @EXPORT_OK anything but use @EXPORT with caution.
       For function and method names use barewords in preference to names prefixed with ampersands
       for the export lists.

       Other module design guidelines can be found in perlmod.

   How to Import
       In other files which wish to use your module there are three basic ways for them to load your
       module and import its symbols:

       "use YourModule;"
           This  imports  all  the symbols from YourModule's @EXPORT into the namespace of the "use"
           statement.

       "use YourModule ();"
           This causes perl to load your module but does not import any symbols.

       "use YourModule qw(...);"
           This imports only the symbols listed by the caller  into  their  namespace.   All  listed
           symbols must be in your @EXPORT or @EXPORT_OK, else an error occurs.  The advanced export
           features of Exporter are accessed like this, but with list entries that are syntactically
           distinct from symbol names.

       Unless  you  want  to use its advanced features, this is probably all you need to know to use
       Exporter.

Advanced Features
   Specialised Import Lists
       If any of the entries in an import list begins with !, : or / then the list is treated  as  a
       series  of  specifications  which  either  add to or delete from the list of names to import.
       They are processed left to right. Specifications are in the form:

           [!]name         This name only
           [!]:DEFAULT     All names in @EXPORT
           [!]:tag         All names in $EXPORT_TAGS{tag} anonymous array
           [!]/pattern/    All names in @EXPORT and @EXPORT_OK which match

       A leading ! indicates that matching names should be deleted from the list of names to import.
       If the first specification is a deletion it is treated as though preceded  by  :DEFAULT.   If
       you  just  want  to  import extra names in addition to the default set you will still need to
       include :DEFAULT explicitly.

       e.g., Module.pm defines:

           our @EXPORT      = qw(A1 A2 A3 A4 A5);
           our @EXPORT_OK   = qw(B1 B2 B3 B4 B5);
           our %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);

       Note that you cannot use tags in @EXPORT or @EXPORT_OK.

       Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.

       An application using Module can say something like:

           use Module qw(:DEFAULT :T2 !B3 A3);

       Other examples include:

           use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
           use POSIX  qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);

       Remember that most patterns (using //) will need to be  anchored  with  a  leading  ^,  e.g.,
       "/^EXIT/" rather than "/EXIT/".

       You  can  say  "BEGIN  {  $Exporter::Verbose=1  }"  to  see  how the specifications are being
       processed and what is actually being imported into modules.

   Exporting Without Using Exporter's import Method
       Exporter has a special method, 'export_to_level' which is used in situations where you  can't
       directly call Exporter's import method.  The export_to_level method looks like:

           MyPackage->export_to_level(
               $where_to_export, $package, @what_to_export
           );

       where  $where_to_export  is  an  integer  telling how far up the calling stack to export your
       symbols, and @what_to_export is an array telling what symbols *to* export  (usually  this  is
       @_).  The $package argument is currently unused.

       For example, suppose that you have a module, A, which already has an import function:

           package A;

           our @ISA = qw(Exporter);
           our @EXPORT_OK = qw($b);

           sub import
           {
               $A::b = 1;     # not a very useful import method
           }

       and you want to Export symbol $A::b back to the module that called package A.  Since Exporter
       relies  on  the  import method to work, via inheritance, as it stands Exporter::import() will
       never get called.  Instead, say the following:

           package A;
           our @ISA = qw(Exporter);
           our @EXPORT_OK = qw($b);

           sub import
           {
               $A::b = 1;
               A->export_to_level(1, @_);
           }

       This will export the symbols one level 'above' the current package - ie: to  the  program  or
       module that used package A.

       Note:  Be  careful  not to modify @_ at all before you call export_to_level - or people using
       your package will get very unexplained results!

   Exporting Without Inheriting from Exporter
       By including Exporter in your @ISA you inherit an Exporter's import()  method  but  you  also
       inherit  several  other  helper  methods  which  you  probably  don't want and complicate the
       inheritance tree.  To avoid this you can do:

         package YourModule;
         use Exporter qw(import);

       which will export Exporter's own import() method into YourModule.  Everything  will  work  as
       before but you won't need to include Exporter in @YourModule::ISA.

       Note: This feature was introduced in version 5.57 of Exporter, released with perl 5.8.3.

   Module Version Checking
       The  Exporter  module will convert an attempt to import a number from a module into a call to
       "$module_name->VERSION($value)".  This can be used to validate that the version of the module
       being used is greater than or equal to the required version.

       For historical reasons, Exporter supplies a "require_version" method that simply delegates to
       "VERSION".   Originally,   before   "UNIVERSAL::VERSION"   existed,   Exporter   would   call
       "require_version".

       Since the "UNIVERSAL::VERSION" method treats the $VERSION number as a simple numeric value it
       will  regard version 1.10 as lower than 1.9.  For this reason it is strongly recommended that
       you use numbers with at least two decimal places, e.g., 1.09.

   Managing Unknown Symbols
       In some situations you may want to prevent certain symbols from  being  exported.   Typically
       this  applies  to  extensions  which  have  functions or constants that may not exist on some
       systems.

       The names of any symbols that cannot be exported should be listed in the @EXPORT_FAIL array.

       If a module attempts to import any of these symbols the Exporter  will  give  the  module  an
       opportunity  to  handle  the situation before generating an error.  The Exporter will call an
       export_fail method with a list of the failed symbols:

         @failed_symbols = $module_name->export_fail(@failed_symbols);

       If the "export_fail" method returns an empty list then no  error  is  recorded  and  all  the
       requested symbols are exported.  If the returned list is not empty then an error is generated
       for  each  symbol and the export fails.  The Exporter provides a default "export_fail" method
       which simply returns the list unchanged.

       Uses for the "export_fail" method include giving better error messages for some  symbols  and
       performing  lazy architectural checks (put more symbols into @EXPORT_FAIL by default and then
       take them out if someone actually tries to use them and an expensive check  shows  that  they
       are usable on that platform).

   Tag Handling Utility Functions
       Since  the  symbols  listed  within  %EXPORT_TAGS  must  also  appear  in  either  @EXPORT or
       @EXPORT_OK, two utility functions are provided which allow you to easily add tagged  sets  of
       symbols to @EXPORT or @EXPORT_OK:

         our %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);

         Exporter::export_tags('foo');     # add aa, bb and cc to @EXPORT
         Exporter::export_ok_tags('bar');  # add aa, cc and dd to @EXPORT_OK

       Any  names which are not tags are added to @EXPORT or @EXPORT_OK unchanged but will trigger a
       warning (with "-w") to  avoid  misspelt  tags  names  being  silently  added  to  @EXPORT  or
       @EXPORT_OK.  Future versions may make this a fatal error.

   Generating Combined Tags
       If several symbol categories exist in %EXPORT_TAGS, it's usually useful to create the utility
       ":all" to simplify "use" statements.

       The simplest way to do this is:

        our  %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);

         # add all the other ":class" tags to the ":all" class,
         # deleting duplicates
         {
           my %seen;

           push @{$EXPORT_TAGS{all}},
             grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS;
         }

       CGI.pm  creates  an  ":all"  tag  which contains some (but not really all) of its categories.
       That could be done with one small change:

         # add some of the other ":class" tags to the ":all" class,
         # deleting duplicates
         {
           my %seen;

           push @{$EXPORT_TAGS{all}},
             grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}}
               foreach qw/html2 html3 netscape form cgi internal/;
         }

       Note that the tag names in %EXPORT_TAGS don't have the leading ':'.

   "AUTOLOAD"ed Constants
       Many modules make use of "AUTOLOAD"ing for constant subroutines to avoid  having  to  compile
       and  waste  memory  on  rarely used values (see perlsub for details on constant subroutines).
       Calls to such constant subroutines are not optimized away at compile time because they  can't
       be checked at compile time for constancy.

       Even  if  a  prototype  is  available  at compile time, the body of the subroutine is not (it
       hasn't been "AUTOLOAD"ed yet).  perl needs to examine both the "()" prototype and the body of
       a subroutine at compile time to detect that it can safely replace calls  to  that  subroutine
       with the constant value.

       A workaround for this is to call the constants once in a "BEGIN" block:

          package My ;

          use Socket ;

          foo( SO_LINGER );  ## SO_LINGER NOT optimized away; called at runtime
          BEGIN { SO_LINGER }
          foo( SO_LINGER );  ## SO_LINGER optimized away at compile time.

       This  forces  the  "AUTOLOAD"  for  "SO_LINGER" to take place before SO_LINGER is encountered
       later in "My" package.

       If you are writing a package  that  "AUTOLOAD"s,  consider  forcing  an  "AUTOLOAD"  for  any
       constants  explicitly  imported by other packages or which are usually used when your package
       is "use"d.

Good Practices
   Declaring @EXPORT_OK and Friends
       When using "Exporter" with the standard "strict" and "warnings" pragmas, the "our" keyword is
       needed to declare the package variables @EXPORT_OK, @EXPORT, @ISA, etc.

         our @ISA = qw(Exporter);
         our @EXPORT_OK = qw(munge frobnicate);

       If backward compatibility for Perls under 5.6 is important, one must  write  instead  a  "use
       vars" statement.

         use vars qw(@ISA @EXPORT_OK);
         @ISA = qw(Exporter);
         @EXPORT_OK = qw(munge frobnicate);

   Playing Safe
       There  are  some  caveats  with the use of runtime statements like "require Exporter" and the
       assignment to package variables, which can be very subtle for the unaware  programmer.   This
       may  happen  for instance with mutually recursive modules, which are affected by the time the
       relevant constructions are executed.

       The ideal way to never have to think about that is to  use  "BEGIN"  blocks  and  the  simple
       import method.  So the first part of the "SYNOPSIS" code could be rewritten as:

         package YourModule;

         use strict;
         use warnings;

         use Exporter 'import';
         BEGIN {
           our @EXPORT_OK = qw(munge frobnicate);  # symbols to export on request
         }

       Or if you need to inherit from Exporter:

         package YourModule;

         use strict;
         use warnings;

         BEGIN {
           require Exporter;
           our @ISA = qw(Exporter);  # inherit all of Exporter's methods
           our @EXPORT_OK = qw(munge frobnicate);  # symbols to export on request
         }

       The  "BEGIN"  will  assure  that  the  loading of Exporter.pm and the assignments to @ISA and
       @EXPORT_OK happen immediately like "use", leaving no room for something to get awry  or  just
       plain wrong.

       With  respect  to  loading  "Exporter" and inheriting, there are alternatives with the use of
       modules like "base" and "parent".

         use base qw(Exporter);
         # or
         use parent qw(Exporter);

       Any of these statements are nice replacements for "BEGIN  {  require  Exporter;  our  @ISA  =
       qw(Exporter); }" with the same compile-time effect.  The basic difference is that "base" code
       interacts  with declared "fields" while "parent" is a streamlined version of the older "base"
       code to just establish the IS-A relationship.

       For more details, see the documentation and code of base and parent.

       Another thorough remedy to that runtime vs. compile-time trap is to use Exporter::Easy, which
       is a wrapper of Exporter that allows all boilerplate  code  at  a  single  gulp  in  the  use
       statement.

          use Exporter::Easy (
              OK => [ qw(munge frobnicate) ],
          );
          # @ISA setup is automatic
          # all assignments happen at compile time

   What Not to Export
       You have been warned already in "Selecting What to Export" to not export:

       •   method names (because you don't need to and that's likely to not do what you want),

       •   anything by default (because you don't want to surprise your users...  badly)

       •   anything you don't need to (because less is more)

       There's  one  more  item  to  add  to this list.  Do not export variable names.  Just because
       "Exporter" lets you do that, it does not mean you should.

         @EXPORT_OK = qw($svar @avar %hvar); # DON'T!

       Exporting variables is not a good idea.  They can change under the hood,  provoking  horrible
       effects  at-a-distance  that  are too hard to track and to fix.  Trust me: they are not worth
       it.

       To provide the capability to set/get class-wide settings,  it  is  best  instead  to  provide
       accessors as subroutines or class methods instead.

SEE ALSO
       "Exporter" is definitely not the only module with symbol exporter capabilities.  At CPAN, you
       may  find a bunch of them.  Some are lighter.  Some provide improved APIs and features.  Pick
       the one that fits your needs.  The following is a sample list of such modules.

           Exporter::Easy
           Exporter::Lite
           Exporter::Renaming
           Exporter::Tidy
           Sub::Exporter / Sub::Installer
           Perl6::Export / Perl6::Export::Attrs

LICENSE
       This library is free software.  You can redistribute it and/or modify it under the same terms
       as Perl itself.

perl v5.38.2                                 2026-08-18                              Exporter(3perl)