my $string = "http://www.ams.net";
$string =~ s!(.*)!<a href='$1'>$1</a>!g; # g für global
print $string;
^Z
<a href='http://www.ams.net'>http://www.ams.net</a><a href=''></a>

my $string = "http://www.ams.net";
$string =~ s!(.+)!<a href='$1'>$1</a>!g;
print $string;
^Z
<a href='http://www.ams.net'>http://www.ams.net</a>

$string = "string\n";
$string =~ s!(.*)!print "($PREMATCH _ {$1} _ $POSTMATCH)";!ge;