my($pattern) = 0;

while (<INPUT>) {
   if ($_ =~ s/$searchPattern1/$replacePattern1/g) {
   $pattern = 1;
   }
   elsif ($_ =~ s/$searchPattern2/$replacePattern2/g) {
   $pattern = 2;
   }
   elsif ($_ =~ s/$searchPattern3/$replacePattern3/g) {
   $pattern = 3;
   }
   print OUTPUT $_;
}