Learn Regex The Hard Way

http://regex.learncodethehardway.org/book/

by QuarkSpark • 14 years ago

187 40 14 years ago

regex.learncodethehardway.org

bstar77• 14 years ago

This is the "Learn X the Hard Way" book I've really been waiting for. Thanks, Zed, for the time and effort on this one. It's a topic that schools seem to completely ignore for some reason, but a skill I find I use on nearly a daily basis.

redslazer• 14 years ago

Its not done yet, its in draft stage and has been available for a while. Im waiting for it to come out fully on a pdf so i can throw my money at him.

mkramlich2• 14 years ago

I'm pretty sure there have been plenty of books and documentation on regexps at least as far back as the 90's. I distinctly remember O'Reilly books on the topic, that far back, to be specific. For a certain generation at least, we haven't been waiting to be able to learn them. It's out there. Though having additional angles of approach is not bad.

zedshaw7• 14 years ago

Mastering Regular Expressions is the book you're thinking of.

goodweeds• 14 years ago

I never liked the O'Reilly approach. At one point I had read 20 of their books and never felt like I learned anything. Some people can learn from references, but I really prefer Zed's "hard way" method which feels a lot like the Programmed Learning methodlogy (http://en.wikipedia.org/wiki/Programmed_learning).

james2vegas• 14 years ago

This being zedshaw, no surprise at the lack of Perl in this book, but what is funny is at http://regex.learncodethehardway.org/book/learn-regex-the-ha... "Imagine if you could write your regular expressions like this: " I don't have to imagine since Perl's regular expression engine has the x modifier to do just that.

bermanoid• 14 years ago

It's funny...when I read that bit, all I could think was, how much nicer would it be if regexes could just be written without the special characters, using sane word-based self-documenting tokens the way we do the rest of our programming, following scoping and quotation rules that actually mesh with the languages we're using them in?

Then it occurred to me that plenty of people have probably written libraries to do exactly that, but nobody uses them because we all already have regexes built-in almost everywhere that we want to use them. Hell, I've never even looked for one, even though I choke back a little vomit every time I introduce a new regex into a codebase because of how much future debugging pain I know they can cause (all but the shortest ones force what's essentially a full context-shift in order to parse, and in reality what usually happens is people scan a regex as one chunk and say "Eh, a regex, it's probably right, hopefully my bug is somewhere else..." until they have some concrete reason to think otherwise).

Sort of a shame, really, that such a problematically condensed syntax won the prize so early on, and now even those of us that hate it are too comfortable with it to look for something better.

zedshaw7• 14 years ago

Regex aren't difficult to learn, it's just nobody teaches them as a language with a base syntax and words to use. If you just sit down and memorize the names of a few symbols, then learn what each does, then it becomes fairly clear.

It's my belief (totally unfounded) that learning a simple symbolic language like regular expressions teaches you how to handle other symbolic languages like mathematics, chemistry, and programming. That's one of the reasons I'm teaching it and trying to get other people to use it.

More importantly though, they are damn handy. As long as you don't abuse them in places where a lexer+parser is better, you can get a lot done with very little regex in very short time.

riffraff2• 14 years ago

you would _love_ perl6 rules.

dmnd• 14 years ago

Ruby and Python (the two languages used at the end of this book) both have expanded mode regexes too.

zedshaw7• 14 years ago

I tried to keep it generic, so most of the regex in the book will work in Perl, Ruby, Python, and the libraries since they all originate from Perl's ideas of PCRE. The choice of using Python was mostly because people had read my other book and probably already had Python.

Also lots of engines have the verbose form, problem is there's been too many Perl hackers writing those god awful huge regex so everyone thinks dense and succinct is the only way to write regex.

masklinn• 14 years ago

Python has the VERBOSE (re.X/re.VERBOSE) modifier as well, it works nicely with raw triple-quoted strings. And I'm guessing it also exists in Ruby.

urbanautomaton• 14 years ago

Perhaps a footnote could mention that this style really is possible in modern regexp implementations? I see chapter 20 is inked in to cover verbose regexps with comments (which is great!), but the current text could give the impression that it's a purely imaginary feature.

lninyo2• 14 years ago

I think some examples of actual strings that the RegEx (in section 0.2) actually does match would be quite instructive.

Also, I think word problems develop an essential skill, namely mapping new problems (described usually in natural language) to mathematical concepts using the symbols. Problems come first, the neat symbolic form comes way after and generally the main problem is mapping a vague problem description to a concrete description using the symbolic language provided by mathematical notation.

alexjgough• 14 years ago

Here one should not forget the past, and look to Jeffrey Friedl's excellent "Mastering Regular Expressions".

theneb• 14 years ago

It's actually a good accompliment to "Mastering Regular Expressions" as in that book Python isn't covered.

leeoniya6• 14 years ago

"Exercise 11: This Or That" sadly still suffers from using examples which necessitate mentioning caveats I pointed out months ago.

https://news.ycombinator.com/item?id=3297996

Even considering the fact that alteration is introduced after the needed concepts of NL and EOL assertions in "Exercise 7: The Beginning And End"

no me gusta :(

zedshaw7• 14 years ago

I already told you that your reason it was busted is wrong. It's not because of NL or EOL, it's because of the order of precedence of the | operator. If you're going to correct me, be right. In fact, someone also posted a solution in the comments, which you also didn't do.

leeoniya6• 14 years ago

i did not say that you were wrong. you are correct. it is the order of precedence that causes the NL/EOL to be treated as part of the alteration.

you are wrong, however, not to mention this alongside examples that specifically display this in an unrelated context, as this is something that is far from obvious. you can

1. easily use different examples or

2. add one line of text that clears this up

on the other hand, the title of the book is to learn regex the hard way, so i'm quite possibly the one who is wrong here. i am not trying to troll, trust me, i respect the work and knowledge you have put into this. but as someone who has been confused by this in the past during my own learning, i see no reason why you think i'm an exception and continue to argue against any clarification or change.

jongraehl2• 14 years ago

When you guys say "NL" you mean "beginning of line", right?

jongraehl2• 14 years ago

"alternation"

leeoniya6• 14 years ago

hehe, yeah, oops. thx.

riffraff2• 14 years ago

I'm curious to see what ends up in "21: Extensions To Avoid".

By the way, from a quick glance, I believe there is no chapter devoted to discuss how the regexp engines work (which is ok) but will there be a section on "when things explode in your face due to exponential behaviour"?

I remember when I first noticed a regex I wrote had a bewhaviour like that and it was kind of enlightening, because earlier I had always assumed all the talk about this things was rather academic :)

zedshaw7• 14 years ago

Yeah, so I thought about making the 2nd half a walk through building a regex engine by first building a lexer, then a parser, then the engine, but I wasn't sure if that'd work to teach regular expression. I think it'd be a great way to really understand how they work (it's how I figured them out), but I'm not sure if other folks would get the same understanding out of it.

tsliwkan• 14 years ago

I think this would be awesome. The mini database and the simple object system were really interesting exercises in Learn C the Hard Way and this would be another great exercise/project for one of your books.

cschep• 14 years ago

Along these lines are there any plans for "learn compilers the hard way" ? Missed that big time in school.

gghh2• 14 years ago

I am looking forward for item 24 "debugging Regex", and I hope it will cover perl's (use re 'debug') or python re.DEBUG flag. I still didn't find a satisfactory document on the web on those features. I'd also like to see something on the eternal diatribe "regexp VS regular grammars", i.e. how the formers substantially differ from the latter. But maybe that's not the right book, having the (sane) "get it done" approach.

jackfoxy• 14 years ago

Zed, Do you have a timeline in mind for filling out the rest of the exercises in the alpha release? Do you call it a beta at that point? I think you're doing great work, btw. Thanks.

jimmytucson• 14 years ago

Thanks for this. I learned Perl about 1.5 years ago and recently took up learning Python. The one thing I find less intuitive about Python than Perl is its syntax around regular expressions.

Learn Regex The Hard Way

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