note 102533 added to function.preg-match

Please, help me!
What is the valid regex for filtering logins?

The login consists only from characters a-z A-Z, 0-9

but there is no whitespaces.

for example

somebody - valid login
somebody123 - valid login
123somebody123 - valid login
et cetera

some body - invalid login

these regexs doesn't works for me

/[0-9A-Za-z]/i 
/[0-9a-Z]/i
/[0-9a-Z^ ]/i
/[0-9a-Z^\s]/i

i use this code

if (preg_match("/[0-9A-Za-z]/i",$login))
{
$ok=1;
}
----
Server IP: 69.147.83.197
Probable Submitter: 178.219.41.66
----
Manual Page -- http://www.php.net/manual/en/function.preg-match.php
Edit        -- https://master.php.net/note/edit/102533
Del: integrated  -- https://master.php.net/note/delete/102533/integrated
Del: useless     -- https://master.php.net/note/delete/102533/useless
Del: bad code    -- https://master.php.net/note/delete/102533/bad+code
Del: spam        -- https://master.php.net/note/delete/102533/spam
Del: non-english -- https://master.php.net/note/delete/102533/non-english
Del: in docs     -- https://master.php.net/note/delete/102533/in+docs
Del: other reasons-- https://master.php.net/note/delete/102533
Reject      -- https://master.php.net/note/reject/102533
Search      -- https://master.php.net/manage/user-notes.php