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Neil Bowers
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again - Reload modules when they change


 use again 'LWP::Simple';             # default import
 use again 'LWP::Simple', [];         # no import
 use again 'LWP::Simple', [qw(get)];  # import only get
 use again 'LWP::Simple', ();         # default import (!!)
 use again 'LWP::Simple', qw(get);    # import only get
 use again;
 require_again 'Foo::Bar';


The again module provides a mechanism for reloading a module if its file has changed since it was first / previously loaded. This can be useful for long-running applications, where new versions of modules might be installed while the application is still running.


use again;

A bare use again; (that is: no import list) will export require_again (and use_again, which always croaks saying you should use use again instead) into your namespace. There is no convenient way to import require_again without importing use_again too.

use again MODULE, [ IMPORTS ];

If you do pass arguments, the first is used with require_again, and all remaining arguments are used to import symbols into your namespace.

When given arguments, use again does not export its own functions.

A single array reference is flattened. If that arrayref contains no elements, the import does not take place.

In mod_perl scripts, this of course only happens when your script is evaled. This happens when your Apache::Registry or Apache::PerlRun script changes, or when your PLP script is requested.

require_again MODULE;

This is the driving force behind again.pm. It requires your module if it has not been loaded with require_again before or it has changed since the last time require_again loaded it.

If you're imported a function from the module, then you'll need to re-import it after calling require_again:

 use again 'Module::Path', qw(module_path);

 ... do some stuff ...


If you don't do this then you'll end up running the version of the function that you first loaded.


Module::Reload provides a class method which checks all loaded modules to see if the file on disk has changed since the module was loaded. It was last updated in 1998, and I haven't tested it.

Class::Unload unloads a class, by clearing out its symbol table and removing it from %INC.

Padre::Unload is part of the Padre IDE. It's similar to Class::Unload, but says it has "a few more tricks up its sleeve". It's not documented though, so just intended for internal use in Padre.




There is no license. This software was released into the public domain. Do with it what you want, but on your own risk. The author disclaims any responsibility.

If you want to (re)distribute this module and need a license, you can redistribute it and/or modify it under the same terms as Perl itself.


Juerd Waalboer <juerd@cpan.org> <http://juerd.nl/>

Documentation updates from Neil Bowers.