Mahantesh Hongal <mailto:[EMAIL PROTECTED]> wrote:
:
: Just I want to place all my subs (functions) in one file i.e., module
: and want to refer as and when it is needed. I can use 'require' for
: this purpose but in require technique code will be included at
: runtime and even if our script is working fine and the sub function
: which we are including through require is having error and then whole
: script will be stopped. So, I want code in such a way that which will
: run indipended of the modules (subs).
What you are describing is called "exporting" (or "importing" --
depending on how you look at it.). There is a module which probably
came with your perl distribution. It is named Exporter.pm and it will
ease building modules like the one you describe. Read its
documentation for more details.
Let's begin writing our new module with a subroutine we will
probably rarely use, but hate to have to rewrite each time we need
it. The truth is, it is not hard to write, just hard to remember.
sub Identity {
return @_;
}
Wow. That's a long one. We are now ready to create the module.
package SpecialSubs;
sub Identity {
return @_;
}
1;
This module is all we really need. Create a file like this
and name it "SpecialSubs.pm". Come back when your done. The "1;" at
the end is very important. It is needed on all modules.
=========
Okay, you're back. Now let's create a script in our favorite
editor and run it.
#!/usr/bin/perl
use strict;
use warnings;
use SpecialSubs;
print SpecialSubs::Identity( 'foo' );
__END__
Prefixing every sub with "SpecialSubs::" could get old quick.
When we "use" a module a series of events occur. One of those events
is running a subroutine named "import" if it is present.
Let's go back to the module and add an "import" sub
package SpecialSubs;
sub import {
print "This is the import sub running automatically\n";;
}
sub Identity {
return @_;
}
1;
We'll also change our script.
#!/usr/bin/perl
use strict;
use warnings;
use SpecialSubs;
__END__
Run this and you'll see that the import sub is called
automatically. We can use the import sub to "import"
subroutines into your script.
The caller() function from perl will tell us the details
about how this module was called.
package SpecialSubs;
sub import {
my( $name_space, $script, $line_number ) = caller();
printf qq(%s "use"d by %s on line %s in package "%s".\n),
'SpecialSubs::import()',
$script,
$line_number,
$name_space;
}
sub Identity {
return @_;
}
1;
Running our script now reveals which package has called
SpecialSubs.pm. We can get just the name space of the caller
with this.
package SpecialSubs;
sub import {
my $name_space = caller();
print $name_space;
}
sub Identity {
return @_;
}
1;
Knowing the name space of the caller, we can import items
into it's name space. We need to use symbolic references here.
Usually, new perl programmers should avoid symbolic references.
package SpecialSubs;
sub import {
my $caller = caller();
*{$caller . '::Identity'} = \&Identity;
}
sub Identity {
return @_;
}
1;
If there were 100 subs in the module this could get a
little long and sometimes we need more control. For example,
we might need just two subs and are now stuck with 98 subs we
don't need. We also didn't do any error checking.
Exporter.pm comes to the rescue. Using this module to
build our modules makes life more simple.
package SpecialSubs;
require Exporter;
@ISA = qw(Exporter);
@EXPORT_OK = qw( Identity );
sub Identity {
return @_;
}
1;
#!/usr/bin/perl
use strict;
use warnings;
use SpecialSubs qw( Identity );
print Identity( 'foo' );
__END__
If you'd rather use strict and warnings in the module
you'll need this.
package SpecialSubs;
use strict;
use warnings;
use vars qw( @ISA @EXPORT_OK );
require Exporter;
@ISA = qw(Exporter);
@EXPORT_OK = qw( Identity );
sub Identity {
return @_;
}
1;
OR:
package SpecialSubs;
use strict;
use warnings;
our( qw( @ISA @EXPORT_OK ) );
require Exporter;
@ISA = qw(Exporter);
@EXPORT_OK = qw( Identity );
sub Identity {
return @_;
}
1;
HTH,
Charles K. Clarkson
--
Mobile Homes Specialist
254 968-8328
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