Stylistic issues aside (you don't need to name $_, you can just do if(m/C B A R/), but I digress), you could probably speed up your code if your test cases are mutually exclusive. That is to say that if 'CBAR' and 'QUAD' will never appear on the same line, you can use elsif instead of if. The elsif will short circuit, thereby eliminating a ton of pattern matches. For more speed, put the more common cases towards the top of the chain of if..elsif..elseif so that it short circuits as early as possible.

HTH,
thor