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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: 0.21s | 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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TheDong ◴[21 Apr 25 11:18 UTC] No.43750628[source]▶
"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)

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1. ◴[21 Apr 25 11:43 UTC] No.43750809[source]▶