regex not working

[kwame123]

this is my code 

$re = '/[^\W][a-zA-Z\d.-]{3,20}/';
if(!preg_match_all($re, $username)){
 do something
  }else{
 do somthing else
}

$username is a $_POST['username'];

when i submit a 3 letter word it works

but when i use symbols like $ and ! and etc it still goes through,

im trying to get a regex where the username is 4-20 characters long and only the alphabet and numbers and

dots and dash but dots and dashs cant be next to each other

 

thx

[Jacques1]

Your regex doesn't say that at all. You have no anchors (which means a substring match is sufficient), and for some strange reason you're using preg_match_all(), as if you expected multiple matches.

 

If you only want to allow dashes and dots as delimiters between alphanumerics, that's

'/\\A[a-z\\d]+(?:[.-][a-z\\d]+)*\\z/i'

Length checks are the job of strlen() or mb_strlen().

Edited June 18, 2017 by Jacques1

[kwame123]

Your regex doesn't say that at all. You have no anchors (which means a substring match is sufficient), and for some strange reason you're using preg_match_all(), as if you expected multiple matches.

 

If you only want to allow dashes and dots as delimiters between alphanumerics, that's

'/\\A[a-z\\d]+(?:[.-][a-z\\d]+)*\\z/i'

Length checks are the job of strlen() or mb_strlen().

oh my goodness thank you so much. not its fixed!