I am creating a username field with Laravel and I'm using RegEx to set the formatting rules.
The rule is: Not only numbers **AND OR** underlines only numbers, chars, and underlines are allowed in general.

Now I came up with this RegEx syntax:
(?!^\d $)^.[a-zA-Z0-9_] $

This works fine until the point where I input stuff like:
____2348734

How can I prevent that? Thanks in advance!

CodePudding user response：

You can use either of

^(?![\d_] $)[a-zA-Z0-9_] $
^(?![\d_] $)\w $

See the regex demo. Also, consider using \z instead of $ to disallow a trailing newline input.

Details:

• ^ - start of string
• (?![\d_] $) - the string cannot only contain digits / underscores
• [a-zA-Z0-9_] / \w - one or more alphanumeric or _ chars
• $ - end of string. (\z will match the very end of string.)