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Some people, when confronted with a problem, think “I know, I’ll use regular expressions.” Now they have two problems.
Regex really isn’t that bad when using named capture groups.
Oh yeah they definitely have uses, but there’s a real tendency for people to go a bit crazy with them. Complex regexen aren’t exactly readable, there’s all kinds of fun performance gotchas, there’s sometimes other tools/algorithms that are more suitable for the task, and sometimes people try to use them to eg. parse HTML because they don’t know that it is literally impossible to use regular expressions to parse languages that aren’t regular
It’s entirely possible to parse HTML in PCRE. You shouldn’t, but it is possible. The language stopped being strictly regular a long time ago and is entirely capable of doing it.
Oh yeah, extensions which make them non-regular definitely can make it possible, but just because it’s now somewhat possible with some regex engines doesn’t mean it’s a good idea
I’ve once written a JS decompiler (de-bundler?) using ~150 regex for step-wise transformations. Worked surprisingly well!
What eldritch beast was summoned as a result?
Well… No new ones, at least? Though it was around that time that I started hearing whispers in the night… “You can use WASM to ship Client-Side PHP”
it is literally impossible to use regular expressions to parse languages that aren’t regular
It’s impossible to parse the whole syntax tree, but that doesn’t mean you can’t get the subset you’re interested in.
Jwz’s 2nd law!
I learned Regex once and now it just works. Only problem for me is using MacOS so the Regex flavors aren’t consistent. But once I sort that, it’s smooth sailing.
Regex feels distinctly eldritch to me. Like, a lot of computing knowledge feels like magic, but regex feels like the kind of magic you get by consorting with dark forces
Blasphemy, that’s not regex that’s just fancy grep
I don’t actually know whether POSIX grep would support named groups :o
Don’t have you have to use the
-Pflag?which is just perl mode
Yes, but perl mode has more features.
I don’t fully disagree but you are walking on a fine line…
any idea what the re in grep stands for?
I really like this approach for doing non trivial regex https://github.com/VerbalExpressions
const tester = VerEx() .startOfLine() .then('http') .maybe('s') .then('://') .maybe('www.') .anythingBut(' ') .endOfLine();I don’t. It may look less like line noise, but it doesn’t unravel the underlying complexity of what it does. It’s just wordier without being helpful.
Edit: also, these alternative syntaxes tend to make some easy cases easy, but they have no idea what to do with more complicated cases. Try making nested capture groups with these, for instance. It gets messy fast.
it doesn’t unravel the underlying complexity of what it does… these alternative syntaxes tend to make some easy cases easy, but they have no idea what to do with more complicated cases
This can be said of any higher-level language, or API. There is always a cost to abstraction. Binary -> Assembly -> C -> Python. As you go up that chain, many things get easier, but some things become impossible. You always have the option to drop down, though, and these regex tools are no different. Software development, sysops, devops, etc are full of compromises like this.
Exactly, at the end of the day it’s about using the right tool for the job. Code that’s clear and declarative is easier to maintain, so it makes sense to default to it, but nothing stops you from using low level constructs if you really need to.
Named groups are nice but can I please define a group more than once because maybe I want to group my data and consolidate values in a logical way without you complaining I have already used a group previously. I know I did, I’m the one telling you, now capture it twice!
Can you actually name capture groups, or this means how you can refer to them by number?
You can use backreferences
\1 \2etc. but you can also give them names explicitly.
it looks like this:(?inner-regex)
Some flavors support it, kotlins doesn’t apparently.TIL thanks!
In modern languages you can name them with labels as well yes. Not sure about the syntax right now. Something like (?label:…) I think
It’s
(?...)and those are the named capture groups referred to in the post.
I don’t see the problem. But that’s probably because my goto-language is perl.
