$bad_words = array('ugly', 'anotherugly');
$good_words = array('ug**','anot******y');
$txt = 'ugly anotherugly';
$txt str_replace($bad_words, $good_words, $txt);

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;

my %words = ( 
	ugly => 'ug**',
	anotherugly => 'anot*******',
);
my $txt = "ugly anotherugly";
$txt =~ s/$_/$words{$_}/g foreach %words;
print $txt;