e.g.

Town\tCounty
Westminster\tGreater London
King's Cross\tGreater London
Mayfair (north)\tGreater London
Mayfair (south)\tGreater London
...

##</code><code>##

Town\tCounty\tVALUE

##</code><code>##

$tmp=(get the file contents);
$tmp=~s/\r//g;
$tmp="\n$tmp\n";

($n,$v)=[got from somewhere, same as list items]
($ctr)=[got from somewhere else]
($rctr)=[count of replacements made]

## attempt 1

if ($tmp=~/^$n\t$v$/) {          
   $tmp=~s/^$n\t$v$/$n\t$v\t$ctr/;
   $rctr++;
} else {

....

##</code><code>##

# attempt 2

   $n=~s/\(/\\(/g;    ## << this works ok!
   $n=~s/\)/\\)/g;
   $n=~s/\'/\\'/g;    ## << same method, NO WORK!</font>

   if ($tmp=~/^$n\t$v$/) {
	$tmp=~s/^$n\t$v$/$n\t$v\t$ctr/;
        $gctr++;
   }