PHP regex pattern for matching username

Question

I'm developing a laravel application where a user can refer to his profile by putting his username in the appropriate form.

Let's see an example:

A user named John can refer to his profile using the following text: @John

I spent several hours trying to understand how regex works, but this pattern is where i've got so far: @([A-Za-z0-9]+)

This pattern perfectly matches the example above, but it also matches other formats that it normally shouldn't.

I need some help creating the perfect pattern.

It should only match a string that starts with the @ symbol. For example: @John, @Sam, @Bill, etc.

It shouldn't match a string that doesn't start with the @ symbol. For example: a@John, something@Sam, 123@Bill, etc.

It should also match those formats that contain more than one @ symbols. For example: @John@, @Sam@something, @Bill@@sometext, etc. In this case the pattern should capture: John@, Sam@something, Bill@@sometext

Thanks for your help and sorry for my bad english.

Answer 1

This should work:

(?<=\s|^)@([\w@]+)

There is a positive lookbehind assertion to make sure the tag is preceded by whitespace, or the start of the string. After that it's just a case of consuming the @ character and putting the username inside a capturing group.

Regex demo

Answer 2

Your regex is almost correct. Firstly, you want to say that your regex should match also the begining of the string. You can achieve that with caret symbol (^):

^@([A-Za-z0-9]+)

Secondly, you want to be able to put the @ sign inside. Now it's easy - just add that symbol inside the brackets.

^@([A-Za-z0-9@]+)

Answer 3

Try /(?:\\s@{1,3})([a-zA-Z@.]+)/i

---

Explain

@ Character. Matches a "@" character (char code 64). {1,3} Quantifier. Match between 1 and 3 of the preceding token.

\\w Word. Matches any word character (alphanumeric & underscore). + Plus. Match 1 or more of the preceding token.

Here is regexr: http://regexr.com/3djhq