Catastrophic Backtracking error validating email address

Question

I need to find a regular expression that validates an email address in the simplest form and the email address should not exceed 250 characters. Here is what I came up with so far.

(?=.{1,250}$)(.+)@(.+){2,}\.(.+){2,}

The problem is this expression works for small email lengths sets. i.e. If I put 10 instead of 250 it will work. If I tested the above expression against large sample it will throw catastrophic backtracking exception. https://regex101.com/r/Dv2j2U/1. Can someone please help me solving this?

but cudos ... i never seen that "catastrophic backtracking" error before — Fallenhero, Feb 21 '17 at 12:26
@rawel more info on catastrophic quantifiers [here](http://www.rexegg.com/regex-explosive-quantifiers.html) — Abdul Hameed, Feb 21 '17 at 12:30
@Fallenhero i tried getting that error on regex101 but couldnt achieve it.. great job rawel — Abdul Hameed, Feb 21 '17 at 12:33
@AbdulHameed it's really not that difficult: https://regex101.com/r/CnI8Kw/1, the article you linked should give you a good insight how to achieve it. — Sebastian Proske, Feb 21 '17 at 12:41
It won't matter in most cases, but `(.+)@(.+)` is also prone to catastrophic backtracking. It would be safer to exclude the `@` character from one of the two groups, e.g. `([^@]+)@(.+)`. — Aran-Fey, Feb 21 '17 at 13:20
If anyone wondering why this is downvoted, I guess it should be that "You should never come up with your own email validation regular expression" But you will never know when you will need one. — rawel, Feb 22 '17 at 00:04

Fallenhero · Accepted Answer · 2017-02-21T12:41:17.327

3

Just replace (.+){2,} with .{2,}

edited Feb 21 '17 at 12:41

answered Feb 21 '17 at 12:35

Fallenhero

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Thanks @Fallenhero for the effort. I was finally able to come up with expression with your help. Working expression for me is (?=^.{1,250}$)(.+)@.{2,}\..{2,} – rawel Feb 22 '17 at 00:35

Catastrophic Backtracking error validating email address

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