Regex to validate username - php

Question

I'm trying to understand what's wrong with this regex pattern:
'/^[a-z0-9-_\.]*[a-z0-9]+[a-z0-9-_\.]*{4,20}$/i'
What I'm trying to do is to validate the username. Allowed chars are alphanumeric, dash, underscore, and dot. The restriction I'm trying to implement is to have at least one alphanumeric character so the user will not be allowed to have a nickname like this one: _-_.
The function I'm using right now is:
function validate($pattern, $string){
return (bool) preg_match($pattern, $string);
}
Thanks.
EDIT
As #mario said, yes,t here is a problem with *{4,20}.
What I tried to do now is to add ( ) but this isn't working as excepted:
'/^([a-z0-9-_\.]*[a-z0-9]+[a-z0-9-_\.]*){4,20}$/i'
Now it matches 'aa--aa' but it doesn't match 'aa--' and '--aa'.
Any other suggestions?
EDIT
Maybe someone wants to deny not nice looking usernames like "_..-a".
This regex will deny to have consecutive non alphanumeric chars:
/^(?=.{4,20}$)[a-z0-9]{0,1}([a-z0-9._-][a-z0-9]+)*[a-z0-9.-_]{0,1}$/i
In this case _-this-is-me-_ will not match, but _this-is-me_ will match.
Have a nice day and thanks to all :)

Answer 1

Don't try to cram it all into one regex. Make your life simpler and use a two step-approach:
return (bool)
preg_match('/^[a-z0-9_.-]{4,20}$/', $s) && preg_match('/\w/', $s);
The mistake in your regex probably was the mixup of * and {n,m}. You can have only one of those quantifiers, not *{4,20} both after another.
Very well, here is the cumbersome solution to what you want:
preg_match('/^(?=.{4})(?!.{21})[\w.-]*[a-z][\w-.]*$/i', $s)
The assertions assert the length, and the second part ensures that at least one letter is present.

Answer 2

Try this one instead:
'/[a-z0-9-_\.]*[a-z0-9]{1,20}[a-z0-9-_\.]*$/i'

Answer 3

Its probably just a matter if finetuning, you could try something like this:
if (preg_match('/^[a-zA-Z0-9]+[_.-]{0,1}[a-zA-Z0-9]+$/m', $subject)) {
# Successful match
} else {
# Match attempt failed
}
Matches:
a_b <- you might not want this.
ysername
Username
1254_2367
fg3123as
Non-Matches:
l__asfg
AHA_ar3f!
sAD_ASF_#"#T_
"#%"&#"E
__-.asd
username
1___
Non-matches you might want to be matches:
1_5_2
this_is_my_name

Answer 4

It is clear to me that you should split this into two checks!
Firstly check that they are using all valid characters. If they're not, then you can tell them that they are using invalid characters.
Then check that they have at least one alpha-numeric character. If they're not, then you can tell them that they must.
Two distinct advantages here: more meaningful feedback to the user and cleaner code to read and maintain.

Answer 5

Here is a simple, single regex solution (verbose):
$re = '/ # Match password having at least one alphanum.
^ # Anchor to start of string.
(?=.*?[A-Za-z0-9]) # At least one alphanum.
[\w\-.]{4,20} # Match from 4 to 20 valid chars.
\z # Anchor to end of string.
/x';
In Action (short form):
function validate($string){
$re = '/^(?=.*?[A-Za-z0-9])[\w\-.]{4,20}\z/';
return (bool) preg_match($re, $string);
}

Answer 6

Try this:
^[a-zA-Z][-\w.]{0,22}([a-zA-Z\d]|(?<![-.])_)$
From related question: Create one RegEx to validate a username

Answer 7

^[A-Za-z][A-Za-z0-9]*(?=.{3,31}$)[a-z0-9]{0,1}([a-z0-9._-][a-z0-9]+)*[a-z0-9.-_]{0,1}$
This will Validate the username
start with an alpha
accept underscore dash and dots
no spaces allowed

Answer 8

Why don't you make it simpler like this?
^[a-zA-Z][a-zA-Z0-9\._-]{3,9}
First letter should be Alphabetical.
then followed by character or symbols you allowed
length of the word should be between 4,10 (as explicitly force the first word)