Using the regex class

It depends how you want to parse the text file. RegEx is usually good for simple parsing, but using automated parser generators with specified grammars, is much better solution. There is a tool called antlr. It has C# version and given a grammar it will generate parser code for it to parse the text. It's LL(k) parser, and the generated code is readable. You can find it at http://www.antlr.org and it's open source. If you're looking just for regex stuff, you should look for DFA (deterministic finite automata) stuff. Most regex engines convert regex expression into DFA or NDFA and just execute the state machine.