Regex Isn't Hard (2023)

Post by vitus » Mon, Apr 21, 2025, 11:51 AM UTC

ninkendo wrote: post #39

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…

Post by michaelt » Mon, Apr 21, 2025, 12:02 PM UTC

vitus wrote: post #42

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.

It's especially ironic given that the title of the post is "Regex Isn't Hard", and then it proceeds to make several (syntactical and logical) errors in the one real-world example. Syntax error aside (there's an extra ] floating around), it's not even close to correct -- it'll match "999.999.999.000.999." among other things, will never match just one digit (there's a missing ?), and always insists on the trailing dot.

Post by thomasmg » Mon, Apr 21, 2025, 12:15 PM UTC

lhamil64 wrote: post #37

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 co…

Post by LaputanMachine » Mon, Apr 21, 2025, 12:18 PM UTC

latexr wrote: post #47

I’m a fan of regular expressions, though I understand why many people wince at the sight. You should avoid showing them to a non-programmer who is interested in learning to code, because they’ll immediately fear programming is intractable. Even as much as I like regex, I wouldn’t recommend this post. One reason is the code style is too close to regular text: > a matches a single character, always lowercase a. That se…

Post by deciduously » Mon, Apr 21, 2025, 12:21 PM UTC

comrade1234 wrote: post #54

lalaithion wrote: post #25

Earlier quoted context omitted.

The author says “any lowercase character” but they mean “any character between the character ‘a’ and the character ‘z’”, which happens to correspond to the lower case letters in English but doesn’t include ü, õ, ø, etc.

I would expect [a-z] to mean any lowercase in any language, not lowercase but only a to z. So I’d get bitten by that one.