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Regex Isn't Hard (2023)

(timkellogg.me)
75 points asicsp | 1 comments | 21 Apr 25 10:35 UTC | HN request time: 0.571s | source
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michaelt ◴[21 Apr 25 11:01 UTC] No.43750496[source]▶
> 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.

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vitus ◴[21 Apr 25 11:33 UTC] No.43750726[source]▶
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.

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1. michaelt ◴[21 Apr 25 12:02 UTC] No.43750946[source]▶
Correct - it'll accept "999.999.999.000.999." but it'll reject "127.0.0.1"