How can I catch accesses to undefined variables/functions/methods?

The AUTOLOAD method, discussed in Autoloading and AUTOLOAD: Proxy Methods, lets you capture calls to undefined functions and methods.

When it comes to undefined variables that would trigger a warning under -w, you can use a handler to trap the pseudo-signal __WARN__ like this: 

    $SIG{__WARN__} = sub {


	for ( $_[0] ) {


	    /Use of uninitialized value/  && do {
		# promote warning to a fatal
		die $_;
	    };


	    # other warning cases to catch could go here;


	    warn $_;
	}


    };