The reason you're getting garbage at the end of your loop is because you're pushing stuff onto @array, then shifting stuff off the front, but looping over @array sequentially. You can't alter the thing you're looping over and expect sane results.

BTW, you don't need to use a C-style for loop to iterate over an array, it's much easier to write it this way:

my @results;
foreach my $addr( @array ) { 
    my $element = lc $addr;
    # mess with $element here
    push @results, $element;
}

return @results;
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You also don't need to reset @hold each time through the loop if you declare it with my, since it will be lexically scoped to the enclosing block. You'll catch a number of other problems if you turn on strict and warnings; put this at the top of your script:

use strict;
use warnings;
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and fix stuff until it stops yelling at you. Finally, the print @array statement at the end of your sub will never get executed because you return on the previous line!

I think that should be enough to get you well on your way. Good luck!