$text = "<tag#1>BLA</tag#2><tag#2>BLA</tag#2><tag#3>BLA</tag#3>";

$number = 1;

while ($text =~ s/<(.+?)#\d>(.+?)<\/(.+?)#\d>/<$1#$number>$2<\/$3#$number>/) {
$number++;
last;
}

print "$text\n";

##</code><code>##

$text = "<FONT face=arial>this is <FONT SIZE=2>TWO</FONT>bla<FONT color=red>red</FONT>bla bla</FONT>";

$text =~ s#<(.+?\s(.+?)=.+?)>(.+?)<\/.+?>#<$1>$3<\/$2>#g;

print "$text\n";