my $pic = 1;
my $key_MS = "R3R3_${pic}_IF";
my $temp = 90;

          for (my $ip = 1; $ip<=100; $ip++) {
             if ($temp == $ip) {
             $pic++;
            }
        }
        print "New pic value is $key_MS\n";


output:New pic value is R3R3_1_IF