PHP preg_match和regex：lowercaps只能用连字符，数字或字母，以及至少6个字符？

I want to accept an input with lowercaps only either with hyphens, numbers, or alphabets, and at least 6 characters. But the regex below accepts Upper case as long as the input is longer than 6 characters.

$user_name = 'BloggerCathrin';

if(!preg_match('/([a-z0-9]{6}|[a-z0-9\-]{6})/', $user_name))
{
    echo 'please use lowercaps only, either with hyphens, numbers, or alphabets, and at least 6 characters.';
}

How can I fix that?

If you pattern needs to match the whole string - from beginning to end - you need to wrap it inside ^ and $:

      /^([a-z0-9]{6}|[a-z0-9\-]{6})$/
start -´                           `- end

From PCRE regex syntax - Meta-characters :

^ - assert start of subject (or line, in multiline mode)
$ - assert end of subject or before a terminating newline (or end of line, in multiline mode)

If you have a six character minimum (and you also can compact), your pattern might look like:

 /^[a-z0-9-]{6,}$/
             ```- minimum: 6, maximum: unspecified (empty)

Anchor your string with ^ at the start and $ at the end.

"/^[a-z0-9-]{6,}$/"