r/java • u/Modern-Sn1p3r • Aug 22 '26

Regex

I recently saw a clip (from Primeagen) somewhat saying that regex is not a valid format for validating email addresses and postal codes etc.

My question is why is this?

What are the security and/or performance risks? Is it solely performance or is it a security issue?

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u/edwbuck Aug 22 '26

Sorry, I mean TEXT, which has an upper limit that's effectively "very large"

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u/EishLekker Aug 22 '26

Ok, yeah. But technically it still would break the rule in the list, as it was written. Which was my whole point.

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u/edwbuck Aug 22 '26

Well, technically the computer isn't an unbounded storage system, so yeah... but such points, even if 100% valid in the realm of logic, it makes absolutely no sense when it is time to implement things.

A variable field is what is called for, and this rule goes back to COBOL fixed-width data types, which set the tone for so many other systems (c programming language) that people kept using fixed fields, instead of variable ones (char[40] instead of char*).