NGINX - url rewrite regular expression

Question

I have the url such as example.com/page.php?username=test. I want to rewrite this url into something like: example.com/test only if test follows the following regual expression: /^[0-9a-zA-Z_-]{1,35}+$/, else 404 page.

Answer 1

This should work:

    location /page.php {
      if ($args ~ "^username=([0-9a-zA-Z_-]{1,35})$")
      {  
        set $username $1;
        rewrite . /$username last;
      }  
      return 404;
    }  

The trick is that in the location directive Nginx matches for the variable $uri, according to the documentation this variable does not include any get arguments. So the only way to achieve your goal is to first match for the uri /page.php, and then check the arguments in an if statement.

The reason why i had to do the set $username $1; instead of directly redirecting to the variable $1 is that the rewrite directive itself matches for sub strings of the given pattern, so it overwrites the $[0-9] variables. So I had to use the temporary $username variable to keep the username.

You might want to do something else than return 404; in the case where somebody gets into the location /page.php but the value of the username parameter does not match the regular expression.