my $f;
$f = $h->{b}{c}{d} if exists($h->{b}{c}) and exists($h->{b}{c}{d});

##</code><code>##

use feature 'state';  # 'use 5.10' or later also gives this automatically
state $f = $h->{b}{c}{d} if exists($h->{b}{c}) and exists($h->{b}{c}{d});