Modules

• A set of related functions and variables in a library file
• A package with the same name as the file

• Perl module files have the extension .pm
• Module names are capitalized (i.e. MyModule.pm)

• Some::Module corresponds to Some/Module.pm

• @EXPORT  : Symbols (functions and variables) that will be exported by default
• @EXPORT_OK  : Symbols that can optionally be exported
• The ampersand in front of a function is optional (and the code is more efficient without it)

Using a module

• Import all symbols that are exported by default:

use Some::Module;

• Import only the specified symbols:

use Some::Module qw($var1 func1);

• Import none of the symbols:

use Some::Module ();

Sample module

package MyModule;   # MyModule.pm

use strict;
use warnings;

BEGIN {
    use Exporter ();                   # Do not import any symbols from Exporter
    our (@ISA, @EXPORT, @EXPORT_OK);

    @ISA = qw(Exporter);

    # Symbols that are exported by default
    @EXPORT = qw($var1 func1);

    # Symbols that are optionally exported
    @EXPORT_OK = qw($var2 func2);
}
our @EXPORT_OK;


# Declare package variables
our ($var1, $var2, $var3);

# Initialize package variables
$var1 = "This is var1\n";
$var2 = "This is var2\n";
$var3 = "This is var3\n";

# Define functions
sub func1 { print "This is func1\n"; }
sub func2 { print "This is func2\n"; }
sub func3 { print "This is func3\n"; }


# Module clean-up code
END {
}

# Main execution of the module starts here
# ...

1;  # Return a true value from the file

Using the sample module

# Import all symbols that are exported by default
use MyModule;

print $var1;
print $MyModule::var2;
print $MyModule::var3;

&func1();
&MyModule::func2();
&MyModule::func3();

# Import only the specified symbols
use MyModule qw($var1 $var2 func1 func2);

print $var1;
print $var2;
print $MyModule::var3;

&func1();
&func2();
&MyModule::func3();

# Import none of the symbols
use MyModule ();

print $MyModule::var1;
print $MyModule::var2;
print $MyModule::var3;

&MyModule::func1();
&MyModule::func2();
&MyModule::func3();