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How do I create a module?

by faq_monk (Initiate)
on Oct 08, 1999 at 00:27 UTC ( #687=perlfaq nodetype: print w/ replies, xml ) Need Help??

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

A module is a package that lives in a file of the same name. For example, the Hello::There module would live in Hello/There.pm. For details, read the perlmod manpage. You'll also find the Exporter manpage helpful. If you're writing a C or mixed-language module with both C and Perl, then you should study the perlxstut manpage.

Here's a convenient template you might wish you use when starting your own module. Make sure to change the names appropriately.

    package Some::Module;  # assumes Some/Module.pm

    use strict;

    BEGIN {
        use Exporter   ();
        use vars       qw($VERSION @ISA @EXPORT @EXPORT_OK %EXPORT_TAGS);

        ## set the version for version checking; uncomment to use
        ## $VERSION     = 1.00;

        # if using RCS/CVS, this next line may be preferred,
        # but beware two-digit versions.
        $VERSION = do{my@r=q$Revision: 1.21 $=~/\d+/g;sprintf '%d.'.'%02d'x$#r,@r};

        @ISA         = qw(Exporter);
        @EXPORT      = qw(&func1 &func2 &func3);
        %EXPORT_TAGS = ( );     # eg: TAG => [ qw!name1 name2! ],

        # your exported package globals go here,
        # as well as any optionally exported functions
        @EXPORT_OK   = qw($Var1 %Hashit);
    }
    use vars      @EXPORT_OK;

    # non-exported package globals go here
    use vars      qw( @more $stuff );

    # initialize package globals, first exported ones
    $Var1   = '';
    %Hashit = ();

    # then the others (which are still accessible as $Some::Module::stuff)
    $stuff  = '';
    @more   = ();

    # all file-scoped lexicals must be created before
    # the functions below that use them.

    # file-private lexicals go here
    my $priv_var    = '';
    my %secret_hash = ();

    # here's a file-private function as a closure,
    # callable as &$priv_func;  it cannot be prototyped.
    my $priv_func = sub {
        # stuff goes here.
    };

    # make all your functions, whether exported or not;
    # remember to put something interesting in the {} stubs
    sub func1      {}    # no prototype
    sub func2()    {}    # proto'd void
    sub func3($$)  {}    # proto'd to 2 scalars

    # this one isn't exported, but could be called!
    sub func4(\%)  {}    # proto'd to 1 hash ref

    END { }       # module clean-up code here (global destructor)

    1;            # modules must return true

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