$pad =~ s/(?:z(.)(?:z.)+)|(?:.(.))/$1$2/g;

##</code><code>##

use strict;
use warnings;

my $pad = "whatever...";

{
    no warnings qw/uninitialized/;
    $pad =~ s/(?:z(.)(?:z.)+)|(?:.(.))/$1$2/g;
}

# here, all warnings are active again.