I lear ned the hard way with the first edition that URLs change more quickly . Once you learn regular expressions, you'll realize that they're an. Learn Regex the Hard Way - Free download as Text File .txt), PDF File .pdf) or read online for free. RegexOne provides a set of interactive lessons and exercises to help you learn regular expressions.
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Learn Regular Expressions the Hard Way Learn RegEx The Hard Way is a fast crash course in regular expressions and text processing . Professional PDF. This book quickly covers the basics of regular-expression syntax, then delves into the mechanics of expression-processing, common pitfalls, performance issues. Regular Expression Tutorial. First Look at How a Regex Engine Works Internally. In following examples, the way the engine works will have a profound.
For example, [[:upper:]ab] matches the uppercase letters and lowercase "a" and "b". An additional non-POSIX class understood by some tools is [:word:], which is usually defined as [:alnum:] plus underscore. This reflects the fact that in many programming languages these are the characters that may be used in identifiers. With most other regex flavors, the term character class is used to describe what POSIX calls bracket expressions. Some languages and tools such as Boost and PHP support multiple regex flavors.
Mastering Regular Expressions is the book you're thinking of. 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: Technically there has always been a harder way available to all of us.
You acquire a book or some other documentation. The terminals on Mac, Windows, Linux have allowed us to do this for decades, as far back as my own childhood, to give one example. So yeah, I think the "hard way" is good, and iterative feedback and experiment is good, and that's been available for a long time even without Zed's things.
I'm still learning new things even in the last few days, using this approach, except without some third-party playbook I have to follow. Learn Redis the hard way? Download it. Install it. Start it. Enter client. Type things.
See what happens. This is fairly obvious. Agreed O'Reilly is probably more famous for their "completeness" rather than effectiveness at teaching. Here one should not forget the past, and look to Jeffrey Friedl's excellent "Mastering Regular Expressions". It's actually a good accompliment to "Mastering Regular Expressions" as in that book Python isn't covered. 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. But maybe that's not the right book, having the sane "get it done" approach.
This Or That" sadly still suffers from using examples which necessitate mentioning caveats I pointed out months ago. The Beginning And End" no me gusta: I already told you that your reason it was busted is wrong. 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. No, you're wrong still. You also are one of those people who thinks the following: You do not need to teach someone everything right away.
You don't even need to teach them everything as long as what you've taught is the foundational elements and those are correct. This attitude is also hyperbolic. The book is not going to destroy the world because you have a problem with one small portion of one exercise that you can't even fix yourself. Finally, you keep saying these things, and you keep asserting you're correct, but I don't see a solution from you. It's in a git repository: If it's soooooo easy to fix and explain then prove me wrong.
Until you offer up your supposedly superior world saving solution I have to assume you're just wrong but can't admit it. Just out of sheer curiosity, what regexp tutorial would YOU recommend? When you guys say "NL" you mean "beginning of line", right? I'm curious to see what ends up in " 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: 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. I think this would be awesome. Along these lines are there any plans for "learn compilers the hard way"? This would drive you crazy, even if you didn't know mat hematics.
Without the symbols of mathematics we'd find mathematics degenerate to one Jacques Derrida style "obscurantisme terroriste" paper after another. They' d be no better than Philosophers!
Thankfully, humans invented symbols to succinctly describe the things that symbo ls are best at describing, and left human languages to describe the rest. The power of symbolic languages is that, once you learn them, they can describe things more quickly and accurately than a human language can. Regular Expressions Are Character Algebra Regular expressions, or regex, is a symbolic language that describe how to ident ify a sequence of integers or, more practically, characters as matching a requ ired set.
Compared to mathematics regular expressions are pathetically tiny. The re's only a few symbols to learn, and they have exact specific meanings. This ma kes them easy to learn, given that you actually put in the time to learn to read and write them. Effectively a regular expression is the algebra equation to a programming langua ge's word problem.
With them you can describe things that would take mountains o f code if you were to write it by hand. This is why they exist, but being symbol ic languages most people simply hate them because most people are never taught h ow to learn a symbolic language.
The truth is each character inside the parenth esis is actually like a whole word or even a phrase.
What trips you up is you're used to reading sentences where there's spaces between whole words and periods that end cohesive thoughts. When you try to read this, you have to stop and teas e the this one "word" apart into what it's actually doing. However, if you've been programming for a while, you're already processing and u nderstanding a symbolic language, just one that's a bit closer to a human langua ge.
What you need to do is take this tiny bit of symbolic literacy skill and tur n it into a real skill at reading symbols.
To do this you need to do what you do when learning any language: Translate it to and from the language you're curren tly know the best. Imagine if you could write your regular expressions like this: You can now say, "Match from the start a set of one or more digits or a -z followed by any digit to the end of the string.
You'll also learn good habits for writing regular expressions, an d more importantly when to not use them. They're handy tools, but like any tool they're for a particular job. The Giants In Tiny Pants Problem The problem that all symbolic languages have is an expert in them, using time an d continuous evolution, can eventually describe everything as one gigantic equat ion.
They start with something simple and go bad as they tack on hack after hack to handle more and more edge cases.
In regular expressions you end up with the infamous infamous Mail:: Address monstrosity. Here's just the top 6 lines of all 82 lines in this one regular expression: This isn't regular expression's fault, it's the fault of people abusing the tool when there's other tools more suitable. In this case, a simple lexer that used smaller regular expressions would work better and most likely be faster and less error prone. More importantly, a lexer could report errors and tell you where s omething failed to pass.
Tools like lex, re2c, and Ragel all make this easier th an the above. I call this the "giant in tiny pants problem" because you're taking something th at's actually a giant complex piece of code, and trying to cram all of it in the tiny pants of a regular expression. In the above example they're trying to cram an email address parser into one a regular expression, and what they end up wit h is not a succinct clean expression, but still a giant bursting at the seams.
Slaying Giants In Tiny Pants With Parsing The key to using regular expressions correctly is to know where their usefulness ends and when you need to bust out a lexer.
You also need to know where a lexer falls down and when a parser is the right tool. When you use regular expression s to simplify creating lexers that feed into simple parsers you then have a set of tools for cleaning and accurately parsing text without going insane. In this book I'm going to subversively teach you parsing, but I'm going to be ve ry practical and straight forward about it.
No crazy e xplanations of push down finite state automata. Just practical code that gets yo u introduced to the basics of parsing, understanding the core theory, and then a ctually using them to get work done.
That means sitting down with each exercise, actually typing all o f the code in, reading about what you did, and doing the extra credit.
You canno t learn these concepts without actually doing the work and practicing them. Othe rwise you might as well just save your money and continue to suck at programming. A good way to do the book is to go "low and slow". Rather than sit down on Satur day and cram 8 exercises out in a 10 hour marathon, you should spend 1 hour a ni ght and do 1 or 2 exercises. Sometimes you'll blaze through exercises and other times you'll get stuck and need to study.
Some exercise you might have to strugg le with for a week before moving on. But, your average should be about 1 a day a nd consistent steady study is more important than cramming. The reason I give this advice is you've got to train and retrain your brain to u nderstand this new language, and the best way to do that is with repetition and practice.
Otherwise you just cheat yourself and end up thinking you've learned s omething when you've really done nothing but become familiar with the material. Finally, do not copy-paste the regex! The text samples I give you are fine to co py paste, but the regex code I have you type you must type them. You have to act ually type it or you won't learn it. This will seem like painful work at first i f you're used to copy-pasting everything, but after a few weeks it'll be easy an d after three months you'll really know the stuff.
Enjoy the book, and if you need help, just email help learncodethehardway.
Exercise 0: The Setup Teaching regular expressions can be difficult because they are typically embedde d into a programming language or a tool like sed. This is compounded by differen ces between most of these implementations. Rather than have you get stuck in var ious different flavors of regex hell, I've created a very small project called R egetron for experimenting with regular expressions.