任何人都可以帮助我使用 PHP 中的正则表达式

Question

I dont have much knowledge on Regular expression. Help me out if i could achieve the below, Username must need to validate this.

1. Only contains alphanumeric characters, underscore and dot
2. Underscore and dot can't be at the end or start of a username
3. Underscore and dot can't be next to each other
4. Underscore or dot can't be used multiple times in a row

I have come up with this regular expression but i cant fulfill all the above.

/(?<![a-z_|.])([a-z](?:[a-z]|_|.(?!_.))+[a-z]|[a-z]{2})(?![a-z_|.])/

Thanks in advance.

Answer 1

You don't need any lookbehind. Simplify your regex to this:

/^[a-zA-Z0-9](?!(?:.*\.){2}|(?:.*_){2}|.*[._]{2})[a-zA-Z0-9_.]*[a-zA-Z0-9]$/

RegEx Demo

Answer 2

One way to rome... (simple and easy version)

if(substr_count($string,'_')<=1 //for rule 4.
    && substr_count($string,'.')<=1 //for rule 4.
    && substr_count($string,'._')===0 //for rule 3.
    && substr_count($string,'_.')===0 //for rule 3.
    && preg_match('/^[^_\.][a-zA-Z]+[^_\.]$/',$string)// for rule 1. & 2.
) {
     echo 'Valid';
}