If you use the concat operator . in its mutator form .= then you don't need to preinitialize the variable. The mutator forms of the plus (+= and ++) and minus (-= and --) operators as well as the concatenation operator are special cased so that they dont raise a warning when the variable they act on is undefined.

use warnings;
use strict;
my ($str,$x,$y,$c,$d);
$str.=chr($_) for 65..90;
$x++;
--$y;
$c += 10;    
$d -= 2;
print "$str $x $y $c $d\n";
__END__
ABCDEFGHIJKLMNOPQRSTUVWXYZ 1 -1 10 -2
[download]

I believe this is because things like

$hash{foo}.=$foo;
next if $dupe{$_}++;
[download]

are so common.

And just to nitpick, but there's no recursion in your example. ;-)

--- demerphq
my friends call me, usually because I'm late....