How do I create a module?

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.
	$VERSION = (qw$Revision: 1.9 $)[1];


	@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 );


    # initalize 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