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Regex Isn't Hard (2023)

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Re: Regex Isn't Hard (2023)

#31

Post by TheDong »

michaelt wrote: post #9

> e.g. This pattern ([0-9][0-9]?[0-9]][.])+ matches one, two or three digits followed by a . and also matches repeated patterns of this. This wold match an IP address (albeit not strictly). I love regular expressions but one thing I've learned over the years is the syntax is dense enough that even people who are confident enough to start writing regex tutorials often can't write a regex that matches an IP address.

"matches an ip address" is a vague enough specification that of course people fail.

Is it what `inet_addr` accept? In that case, "1", "0x1", "00.01", "00000.01", and more are all ip addresses. `ping` accepts all of em anyway.

Is a valid ipv6 address one with the square brackets around it? Is "::1" a valid ip address? What about "fe80::1%eth2"? ping accepts both of these on my machine (though probably not on yours, since you probably don't have an eth2 interface)

Re: Regex Isn't Hard (2023)

#32

Post by throw-qqqqq »

TrackerFF wrote: post #10

Confession: Regex knowledge is one of those things I've let completely atrophy after integrating LLMs into my workflow. I guess if the day comes that AI/ML models suddenly disappear, or become completely unavailable to me, I'll have to get into the nitty gritty of Regex again...but until that time, it is a "solved problem" for my part.

IMO it’s a “language” you need to understand in order to use.

Just like you wouldn’t copy/paste any random snippet into your source code if you don’t understand exactly what it does.

I see a lot of broken regex at work from people who use regular expressions but don’t understand them (for various reasons).

It used to come with a “found this on stackoverflow”-excuse, but mostly now it’s “AI told me to use this” instead.

Re: Regex Isn't Hard (2023)

#33

Post by stavros »

michaelt wrote: post #9

> e.g. This pattern ([0-9][0-9]?[0-9]][.])+ matches one, two or three digits followed by a . and also matches repeated patterns of this. This wold match an IP address (albeit not strictly). I love regular expressions but one thing I've learned over the years is the syntax is dense enough that even people who are confident enough to start writing regex tutorials often can't write a regex that matches an IP address.

Well, it depends on how specific you want to be. You could do `.*`, and this will match an IP address, or you can be as specific as trying to specify number ranges digit by digit, which is so complicated that it doesn't merit a "can't even".

Also, `16843009` is an IP address, try pinging it.

Re: Regex Isn't Hard (2023)

#34

Post by fragmede »

kelafoja wrote: post #30
gwd wrote: post #21

So my brother doesn't code for a living, but has done a fair amount of personal coding, and also gotten into the habit of watching live-coding sessions on YouTube. Recently he's gotten involved in my project a bit, and so we've done some pair programming sessions, in part to get him up to speed on the codebase, in part to get him up to speed on more industrial-grade coding practices and workflows. At some point we ne…

My problem is that regexes are write-only, unreadable once written (to me anyway). And sometimes they do more than you intended. You maybe tested on a few inputs and declared it fit for purpose, but there might be more inputs upon which it has unintended effects. I don't mind simple, straight-forward regexes. But when they become more complex, I tend to prefer to write out the procedural code, even if it is (much) lo…

You know you can write comments in your code where the regexp is, right?

Re: Regex Isn't Hard (2023)

#36

Post by NikkiA »

TheDong wrote: post #31
michaelt wrote: post #9

> e.g. This pattern ([0-9][0-9]?[0-9]][.])+ matches one, two or three digits followed by a . and also matches repeated patterns of this. This wold match an IP address (albeit not strictly). I love regular expressions but one thing I've learned over the years is the syntax is dense enough that even people who are confident enough to start writing regex tutorials often can't write a regex that matches an IP address.

"matches an ip address" is a vague enough specification that of course people fail. Is it what `inet_addr` accept? In that case, "1", "0x1", "00.01", "00000.01", and more are all ip addresses. `ping` accepts all of em anyway. Is a valid ipv6 address one with the square brackets around it? Is "::1" a valid ip address? What about "fe80::1%eth2"? ping accepts both of these on my machine (though probably not on yours, si…

square brackets around an IP address predates IPv6, it was/is? used to bypass DNS lookups and some (very) old programs required IP addresses inside [...] otherwise they were assumed to be a domain name with all the rules that implied.

Re: Regex Isn't Hard (2023)

#37

Post by lhamil64 »

thomasmg wrote: post #23

For me, the main problem of the Regex syntax is the escaping rules: Many characters require escaping: \ { } ( ) [ ] | * + ? ^ $ . And the rules are different inside square brackets. I think it would be better if literal text is enclosed in quotes; that way, much less escaping is needed, but it would still be concise (and sometimes, more concise). I tried to formulate a proposal here: https://github.com/thomasmueller/…

One thing I noticed with the example `['0-9a-f']`

Doesn't this go against the "literals are enclosed in quotes" idea? In this case, you have a special character (`-`) inside a quoted string. IMO this would be more consistent: `['0'-'9''a'-'f'']`, maybe even have comma separation like `['0'-'9','a'-'f'']`. This would also allow you to include the character classes like `[d,'a'-'f'']` although that might be a little confusing if you're used to normal regex.

Re: Regex Isn't Hard (2023)

#38

Post by [deleted] »

fragmede wrote: post #34
kelafoja wrote: post #30

Earlier quoted context omitted.

My problem is that regexes are write-only, unreadable once written (to me anyway). And sometimes they do more than you intended. You maybe tested on a few inputs and declared it fit for purpose, but there might be more inputs upon which it has unintended effects. I don't mind simple, straight-forward regexes. But when they become more complex, I tend to prefer to write out the procedural code, even if it is (much) lo…

You know you can write comments in your code where the regexp is, right?

[deleted]

Re: Regex Isn't Hard (2023)

#39

Post by ninkendo »

michaelt wrote: post #9

> e.g. This pattern ([0-9][0-9]?[0-9]][.])+ matches one, two or three digits followed by a . and also matches repeated patterns of this. This wold match an IP address (albeit not strictly). I love regular expressions but one thing I've learned over the years is the syntax is dense enough that even people who are confident enough to start writing regex tutorials often can't write a regex that matches an IP address.

Writing one correctly is pretty complicated task if you’re trying to write a simple tutorial… off the top of my head, you’d need:

    (
      (
      25[0-5] # 250-255
      |
      2[0-4][0-9] # 200-249
      |
      1[0-9]{2} # 100-199
      |
      [1-9][0-9] # 10-99
      |
      [0-9]
      )
      \.
    ){3}
    (
    25[0-5] # 250-255
    |
    2[0-4][0-9] # 200-249
    |
    1[0-9]{2} # 100-199
    |
    [1-9][0-9] # 10-99
    |
    [0-9]
    )
… but without all the nice white space and comments, unless you’re willing to discuss regex engines that let you do multi-line/commented literals like that… I think ruby does, not sure what other languages.

The problem is that expressing “an integer from 0-255” is surprisingly complicated for regex engines to express. And that’s not even accounting for IP addresses that don’t use dots (which is legal as an argument to most software that connects to an IP address), as other commenters have pointed out.

Re: Regex Isn't Hard (2023)

#40

Post by qiine »

throw-qqqqq wrote: post #32
TrackerFF wrote: post #10

Confession: Regex knowledge is one of those things I've let completely atrophy after integrating LLMs into my workflow. I guess if the day comes that AI/ML models suddenly disappear, or become completely unavailable to me, I'll have to get into the nitty gritty of Regex again...but until that time, it is a "solved problem" for my part.

IMO it’s a “language” you need to understand in order to use. Just like you wouldn’t copy/paste any random snippet into your source code if you don’t understand exactly what it does. I see a lot of broken regex at work from people who use regular expressions but don’t understand them (for various reasons). It used to come with a “found this on stackoverflow”-excuse, but mostly now it’s “AI told me to use this” instea…

yeah programmers famously understands all the random boilerplate incantations they copy past in their code to get things going.

totally definitively

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