use strict;
use warnings;

my %words = ( 
    ugly => 'ug**',
    anotherugly => 'anot*******',
);
my $txt = "ugly anotherugly";
my @words = split / /, $txt; # largely simplified, you have to count ,.:; etc
for my $i (0 .. $#words) {
	$words[$i] = $words{$words[$i]} if (exists($words{$words[$i]}))
}
print join(' ', @words);