Regex to validate username not working

Question

I have this regex:

/^[A-z0-9\._-]{3,24}+$/i

This is supposed to only match a string between 3 and 24 characters long, and only with the characters a-z, A-Z, 0-9, and then also the . _ and - characters.

The problem is this is also matching strings like "^_^". Someone just created a username with exactly that, so this is definitely a problem! Can anyone spot the problem with my regex?

According to regexr, your pattern has a syntax error; strange why PCRE doesn't seem to care about it. — Ja͢ck
– Ja͢ck, Commented Jun 11, 2014 at 17:59

anubhava · Accepted Answer · 2014-06-11 18:04:24Z

3

Use this regex:

/^[\w.-]{3,24}$/

A-z is not same as [A-Za-z] as it also includes other characters such as ^ (thanks Jack)

Also remove extra quantifier + after {3,24} which means one or more instances of whole string.

PS: I have also shortened your regex to use \w instead of [A-Za-z0-9_]

edited Jun 11, 2014 at 18:04

answered Jun 11, 2014 at 17:46

anubhava

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5 Comments

Gavin Over a year ago

Awesome. Nice and simple! Thanks. I have to wait a couple more minutes before I can accept the answer.

Ja͢ck Over a year ago

Actually, the + has no ill effects (even though it shouldn't be there). What you have "masked" as shortening the regex is actually the fix, because the A-z range includes ^ :)

anubhava Over a year ago

@Jack: Thanks I overlooked that part, added in my answer.

Gavin Over a year ago

wow, i thought A-z was a-z and A-Z. are all the special characters included in A-z?

anubhava Over a year ago

A-z includes all characters in the range from 65 to 122 in ASCII table

mifi79 · Accepted Answer · 2014-06-11 18:28:21Z

2

You do not need the + as you are specifying a range of lengths with the {3,24}

/^[A-z0-9\._-]{3,24}$/i

As was pointed out in the comments below, A-z matches the ^ character, as well. In this case A-Za-z would be better; however, the answer above with \w.- is the most elegant by far.

edited Jun 11, 2014 at 18:28

answered Jun 11, 2014 at 17:47

mifi79

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2 Comments

Ja͢ck Over a year ago

This still matches "^_^".

mifi79 Over a year ago

You are correct, I should not have used A-z in this case, rather A-Za-z. But, frankly, I consider @anubhava's answer more elegant anyway.

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