#!/usr/bin/perl -w
$| = 1;
use strict;
use warnings;
print "Content-Type: text/html\n\nHallo!<br><br>";
my @error;
local $SIG{__WARN__} = sub {
        push @error,shift;
};
print "Vorher: @error<br>\n";
require 'test2.pl';
&fehlersub ('foo');
print "Nachher: @error<br>\n";

Hallo!

Vorher: 
Nachher: Use of uninitialized value in addition (+) at test2.pl line 6. Argument "foo" isn't numeric in addition (+) at test2.pl line 6.