In this case your best bet would be to declare my (@array1, @array2) before the for loop if you want them to be available to your subroutines.

You are not having a problem with undef, you are having a problem variable scoping.

As others have mentioned, you should be using strict - you said it won't help you solve the problem, but how can you solve the problem when you clearly don't understand what the problem is? Using strict will help you figure out what the problem is so you can at least look in the right direction.

Here's what I used to test your code: 
#!/usr/bin/perl

use strict;

foreach my $item ('top', 'heavy', 'fool') {
    my (@array1, @array2);

    a_function($item);

    print "@array1\n";
    print "@array2\n";
}

sub a_function {
    my $item = shift;

    push @array1, 'crap';
    push @array2, 'dumb';
}

[download]
This gave me errors like this: 
Global symbol "@array1" requires explicit package name at ./test_loop.
+pl line 18.
Global symbol "@array2" requires explicit package name at ./test_loop.
+pl line 19.
Execution of ./test_loop.pl aborted due to compilation errors.

[download]
This clearly tells me that the subroutine is looking for global variables. Declaring them as my inside a loop doesn't create global variables. So moving them to the top, like this, works fine: 
...
my (@array1, @array2);

foreach my $item ('top', 'heavy', 'fool') {
...

[download]

In reply to Re: The weirdest problem with undef by saberworks
in thread The weirdest problem with undef by insaniac

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