my $text = 'this is text with a link to http://www.perl.com and to www.perldoc.com'; 
 
$text =~ s!(^|\s)(http://\S+)!<a href="$2">$2</a>!ig;   # get all 'http://' links 
$text =~ s!(^|\s)(www\.\w+\.\S+)!<a href="http://$2">$2</a>!ig;   # get anything that simply starts 'www.' 
 
print $text;