RewriteRule different pages per user - php

Question

I am deciding to create separate profile links for each user who registers on the website. I am using the .htaccess file RewriteRule to achieve this. The url I want to achieve should look something like www.domain.com/username. (I don't want www.domain.com/users/username)
Now the problem is, if I add a rule like RewriteRule ^(.*)$ /users.php?username=$1
it will matchup all URL addresses for www.domain.com, which may direct to any path. Even if I would like to visit www.domain.com/about page, it will be redirected to
www.domain.com/users.php?username=about, which I don't want. (Even if the requests was www.domain.com/products/abc)
I could apply filters in my users.php to filter such usernames, or if a username is not found in database, redirect to the page, but this means I have to change filters every time I decide to add a new page in my directory (in this case, any). Also, all traffic will be directed through 1 page, which may cause a performance problem.
Please suggest a way to achieve this, as There are websites that work like this. A possible RewriteRule or PHP code to achieve this.

Answer 1

You can use this rule in your root .htaccess:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(\w+)/?$ /users.php?username=$1 [L,QSA]

Answer 2

I always use just simple rewrite as below:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule (.*)(.*)/?$ index.php
All traffic is redirected to index.php and using php I can run specific controllers depending on url. You should also think about. Almost all frameworks use such rule.
Then in your PHP file you should examine
$_SERVER['REQUEST_URI']
variable to route request to specific controllers