I have a snippet of code the output of which makes no sense to me: 
#!/usr/bin/perl

use strict;
use warnings FATAL => 'all';

while (reverse <DATA>) {
    warn defined($_) ? "defined\n" : "undefined\n";
    next unless defined($_);
    warn "$_\n";
}

exit 0;

__DATA__
this is line 1
this is line 2
this is line 3

[download]
The DATA is just for convenience. I see the same output is produced if I use STDIN, and that output is: 
undefined
Use of uninitialized value in reverse at text.pl line 6, <DATA> line 3
+.

[download]

If I change the while loop to foreach, then I do not see this odd behavior, but in my real world code, I have a much larger data set, and I would like to keep the memory footprint lower (i.e., see related).

Can someone tell me what is actually happening here? Thanks much!

In reply to Uninitialized value in reverse by Nordikelt

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