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Regular Expressions – Mastering Lookahead and Lookbehind

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Re: Regular Expressions – Mastering Lookahead and Lookbehind

#11

Post by Tobba_ »

filipmandaric wrote: post #6
paulryanrogers wrote: post #3

While useful to some I think advanced RE are like mixing in Perl or playing code golf with production code. They tend to make code harder to read. My preference in such cases is for multiple separated or longer REs (which can be at least split in the surrounding code) and each part named or heavily commented. Of course it's always worthwhile to consider non-RE solutions if the problem can be broken down enough. EDIT:…

Fair enough, but I really think the benefits of advanced regular expressions are underappreciated in non-production and even non-application contexts. Laypeople (and occasionally even developers) are impressed when you show them how to search through a document or file system using a really complicated pattern, where it would have taken several iterations of data manipulation to achieve the same result without using…

It'd help a lot if the grammar was actually readable. Combinations like .* don't visually "read" like a single unit, and then to make everything worse you often need a crazy amount of backslashes.

I'm not sure how you could fix that without introducing completely new characters or color-coding parts of the expression though.

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#12

Post by freedomben »

paulryanrogers wrote: post #3

While useful to some I think advanced RE are like mixing in Perl or playing code golf with production code. They tend to make code harder to read. My preference in such cases is for multiple separated or longer REs (which can be at least split in the surrounding code) and each part named or heavily commented. Of course it's always worthwhile to consider non-RE solutions if the problem can be broken down enough. EDIT:…

I agree, with regards to production code. However, I find that I use regular expressions constantly many many times a day to grep through my code locally looking for particular things. It comes in very handy to know the advanced tools when you are looking for something unusual. Grep may be my most important programming tool next to vim.

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#13

Post by freedomben »

Tobba_ wrote: post #11
filipmandaric wrote: post #6

Earlier quoted context omitted.

Fair enough, but I really think the benefits of advanced regular expressions are underappreciated in non-production and even non-application contexts. Laypeople (and occasionally even developers) are impressed when you show them how to search through a document or file system using a really complicated pattern, where it would have taken several iterations of data manipulation to achieve the same result without using…

It'd help a lot if the grammar was actually readable. Combinations like .* don't visually "read" like a single unit, and then to make everything worse you often need a crazy amount of backslashes. I'm not sure how you could fix that without introducing completely new characters or color-coding parts of the expression though.

The back slashes for escaping are absolutely awful. This is one of the worst things about Java.

It's much better in languages with regex literals like Ruby and JavaScript.

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#14

Post by girvo »

paulryanrogers wrote: post #3

While useful to some I think advanced RE are like mixing in Perl or playing code golf with production code. They tend to make code harder to read. My preference in such cases is for multiple separated or longer REs (which can be at least split in the surrounding code) and each part named or heavily commented. Of course it's always worthwhile to consider non-RE solutions if the problem can be broken down enough. EDIT:…

I agree. Usually, I end up leaning on PEGs instead:

https://nim-lang.org/docs/pegs.html

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#15

Post by Someone1234 »

qiqitori wrote: post #8
filipmandaric wrote: post #2

Most of the time I mention the topic of regular expressions to other developers, I usually hear self-critical commentary like "oh, I'm terrible at regex", and rarely anyone who loves them. I think they're great though, if you take the time to understand them. They're something like a Swiss Army knife for programming.

I think everyone who doesn't know regex should make learning regex a priority. (However, I find that lookahead and lookbehind in particular do not tend to come in handy very often. So maybe just make a mental note that this exists and then look it up when you need it.) Just learn the basics and maybe take a very quick look at the theory, finite automata (maybe the name puts people off, but its just a couple of circle…

Which version of RegEx? I've "learned" RegEx two or three times and then switched language/platform and had everything I previously learned no longer work reliably.

You might think I am just talking about Microsoft's quirky implementation but even in the Linux-sphere it isn't consistent see:

http://www.greenend.org.uk/rjk/tech/regexp.html

You take a complex format string which was design to use the fewest characters instead of with clarity in mind, you then have every major application and library diverge on basic support and spec for features, and then you have all of them hack on support for UNICODE in their own unique way.

Regular Expressions likely won't ever die, but I for one would happily switch to an alternative with better readability, UNICODE support from day zero, and fewer niche features to keep things uniform. I'm tired of re-learning RegEx only to have everything I've learned either be forgot or not work the second I app switch.

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#17

Post by testestx »

jstarfish wrote: post #5
filipmandaric wrote: post #2

Most of the time I mention the topic of regular expressions to other developers, I usually hear self-critical commentary like "oh, I'm terrible at regex", and rarely anyone who loves them. I think they're great though, if you take the time to understand them. They're something like a Swiss Army knife for programming.

They're definitely useful, and I can cobble them together to get lots of otherwise tedious and complex parsing tasks done, but when I come back to them a week later I have no idea what the hell the pile of wingding vomit I wrote was supposed to do. I find myself writing simpler ones and tying them together with app code just for sanity's sake.

> I find myself writing simpler ones and tying them together with app code just for sanity's sake.

Or just use PEG, parser combinators, or other more readable parsing abstractions

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#18

Post by stochastic_monk »

Retra wrote: post #7
filipmandaric wrote: post #2

Most of the time I mention the topic of regular expressions to other developers, I usually hear self-critical commentary like "oh, I'm terrible at regex", and rarely anyone who loves them. I think they're great though, if you take the time to understand them. They're something like a Swiss Army knife for programming.

A programmer saying they are terrible at regex is like a mathematician saying they are terrible at algebra.

I’m not terrible at it, but while useful in general, I rarely use regular expressions in the core programs I develop.

I think the automata theory behind them is more important to know than proficiency with specific regular expression implementations.

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#19

Post by kbenson »

Someone1234 wrote: post #15
qiqitori wrote: post #8

Earlier quoted context omitted.

I think everyone who doesn't know regex should make learning regex a priority. (However, I find that lookahead and lookbehind in particular do not tend to come in handy very often. So maybe just make a mental note that this exists and then look it up when you need it.) Just learn the basics and maybe take a very quick look at the theory, finite automata (maybe the name puts people off, but its just a couple of circle…

Which version of RegEx? I've "learned" RegEx two or three times and then switched language/platform and had everything I previously learned no longer work reliably. You might think I am just talking about Microsoft's quirky implementation but even in the Linux-sphere it isn't consistent see: http://www.greenend.org.uk/rjk/tech/regexp.html You take a complex format string which was design to use the fewest characters…

For the most part, it's just a matter of knowing if you're using POSIX Basic Regular Expressions (BRE), POSIX Extended Regular Expressions (ERE), or Perl regular expressions.

Learn those, or at least the main differences between them, and the vast majority of the regular expression engines in software you use will become more recognizable.

Re: Regular Expressions – Mastering Lookahead and Lookbehind

#20

Post by keithnz »

filipmandaric wrote: post #2

Most of the time I mention the topic of regular expressions to other developers, I usually hear self-critical commentary like "oh, I'm terrible at regex", and rarely anyone who loves them. I think they're great though, if you take the time to understand them. They're something like a Swiss Army knife for programming.

I love regex. Not just for doing pattern matching in code, but for searching and data transformation in editors and tools.

But yes, lots of people do seem to do the "I suck at regex". Even when I notice people do crazy long winded transformations by hand which I then do within seconds. Still doesn't seem enough motivation for them to learn them properly.

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