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submitted 2 weeks ago* (last edited 2 weeks ago) by NateNate60@lemmy.world to c/programmerhumor@lemmy.ml

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^.?$|^(..+?)\1+$

Matches strings of any character repeated a non-prime number of times

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[–] RegalPotoo@lemmy.world 10 points 2 weeks ago* (last edited 2 weeks ago) (2 children)

Something like

!"A line with exactly 0 or 1 characters, or a line with a sequence of 1 or 3 or more characters, repeated at least twice"!<

[–] naonintendois@programming.dev 8 points 2 weeks ago

You're misreading the ..+? part. That means 2 or more characters, non greedy.

[–] NateNate60@lemmy.world 3 points 2 weeks ago (1 children)

It's a line with a sequence of two or more characters repeated at least twice.

[–] MummifiedClient5000@feddit.dk 4 points 2 weeks ago (1 children)

Only the part after the pipe character. The pipe character works as an "or" operator. RegalPotoo is right.

[–] NateNate60@lemmy.world 3 points 2 weeks ago (1 children)

They said—

A line with exactly 0 or 1 characters, or a line with a sequence of 1 or 3 or more characters, repeated at least twice

Note—

...or a line with a sequence of 1 or 3 or more characters, repeated at least twice

It should be—

...or a line with a sequence of 2 or more characters, repeated at least twice

The regex in the post will match "abab". Their original description (line 2 of this comment) will not match "abab".

[–] MummifiedClient5000@feddit.dk 4 points 2 weeks ago

I agree, you're right about the part after the pipe and RegalPotoo's explanation was not entirely correct.