regex expression logic

Question

Regex expressions seems cocumbersome, they always drive me mad when trying to build it up. And i end up asking for help. But once i am given the result it looks really coool. Gurus, is there a way to go about it to break it up.

Answer 1

Yuo can start with tutorials at Regular-Expressions.info which provide a good starting point. The reference there is also invaluable as are the explanations how the regex engine works behind the scenes.

Actually, the fundamentals aren't that hard to grasp and once you got them it's not too hard. However, reading complex regular expressions is more like an arcane art; it can get pretty unwieldy quickly.

Answer 2

This tool might help : http://www.gskinner.com/RegExr/

Answer 3

I could not completely understand your question but if you are looking for good and easier tutorial to get a tight fist on the regex then phpro.org has a great tutorial about it.

Answer 4

This is my favorite reg ex site regexlib

Answer 5

Learning regular expressions requires you to start thinking a bit differently. The syntax is not important, what's crucial is learning that a regex is a way to describe a pattern. Of course you have to consider that you're explaining it to someone (a machine) which is by itself quite dumb, so you have to be very thorough and not assume anything.

Example: you don't look for a word, you look for a sequence of characters which you know can be in a word. You know it, but the machine doesn't, so you have to be specific (well, there are shortcuts, but that's not the point).

So learn to think character-wise instead of the abstract concepts familiar in natural language, and above all practice a lot.

I won't add links as they are already mentioned in other answers. Good luck, regexp are fun!

Answer 6

Not sure what you mean by "break it up", but here are a couple regex tutorials:

The absolute bare minimum every programmer should know about regular expressions

Extreme regex foo: what you need to know to become a regular expression pro

Regulator is good, free tool that helps you to write regular expressions.

Answer 7

Doing web dev I have to do validation a lot. I usually have http://www.regexpal.com/ open in a tab somewhere. That site, combined with a tutorial, combined with a specific problem to solve is how I learned.

Answer 8

I recommend Expresso. Registration is needed after 30 days but it's completely free. It comes with a regex library and includes the author's 30 minute regex tutorial.

RegexBuddy is another popular tool but it's not free. You can view some demos here.

I suggest you go through the tutorial and other helpful sites mentioned so far. Start off with simple patterns and understand them, then move on from there. It's tricky at first, and you need to understand what to look for to design a pattern that matches it.

@gbacon mentioned the most popular book so I won't mention it again. A recent one that has good reviews is the Regular Expressions Cookbook.

Answer 9

Learn to think like the machine by reading How Regexes Work by Mark Dominus. For more, go with Mastering Regular Expressions by Jeffrey Friedl.