Problem about substitution..

[Remy Guo]

hi folks,
i've got problem when trying to perform a substitution.

the text file i want to process is like this:
...
XXXXXX  {
ABDADADGA
afj*DHFHH
}  (a123)
XXDFAAF {
af2hwefh
fauufui
}  (b332)
...

i want to match the content in the parenthesis (a123 and b332, here) and
replace them with a sorted number (0;0,  0;1,  0;2,  .... 0; 255,  1;0,
1;1, ...1; 255, for example), so i wrote the script like this:
     if (m/\}.*\(.*\)/)
     {
             $j++;
             if ($j >= 255)
             {
                 $i++;
                 $j = 0;
             }

             $_ =~ s/163//;
      }

now the problem is that, i'm sure the matching
regex successfully matches the line that i want, but the subsitution just
don't happen.  why?...
need your help....thanks!

- Remy