URL RewriteCond

The RewriteCond directive

The cannonic documentation about the Apache directives can be found here Apache HTTP Server Version 1.3 - Module mod_rewrite - URL Rewriting Engine. Another very useful help is given in the page Apache HTTP Server Version 2.0 - URL Rewriting Guide.

Important: This page is designed to teach you the basics of the RewriteRule directive. Please refer to the cannonic pages to get a full approach.

The RewriteCond directive allow to specify the condition(s) of an URI rewriting.

RewriteCond TestString CondPattern Flag (optionnal)

“TestString” is the string to be tested. It can be many things, but for a start, we will test Server-Variables. These are variables of the form: 

%{NAME_OF_VARIABLE}

 where NAME_OF_VARIABLE can be a string taken from the following list:

HTTP headers:

HTTP_USER_AGENT (e.g. Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0)

HTTP_REFERER (e.g. The location from which the request has been issued.)

HTTP_COOKIE (e.g. a session cookie)

HTTP_FORWARDED

HTTP_HOST (e.g. www.html4.com)

HTTP_PROXY_CONNECTION

HTTP_ACCEPT (e.g. text/xml,application/xml,application/xhtml+xml,text/html;q=

0.9,text/plain;q=0.8,image/png,*/*;q=0.5)

connection & request:

REMOTE_ADDR (e.g. 82.228.162.118)

REMOTE_HOST (e.g. sp137-1-82-228-162-118.fbx.proxad.net)

REMOTE_USER

REMOTE_IDENT

REQUEST_METHOD (e.g. GET)

SCRIPT_FILENAME (e.g. /home/httpd/vhosts/html4.com/httpdocs/test.php)

PATH_INFO

QUERY_STRING (e.g. the parameters following the HTTP_REFERER - and not “HTTP_REFERER + any parameters” as I wrote here before)

AUTH_TYPE

server internals:

DOCUMENT_ROOT (e.g. /home/httpd/vhosts/html4.com/httpdocs)

SERVER_ADMIN (e.g. webmaster[at]html4.com)

SERVER_NAME (e.g. www.html4.com)

SERVER_ADDR (e.g. 66.98.134.64)

SERVER_PORT (e.g. 80)

SERVER_PROTOCOL (e.g. HTTP/1.1)

SERVER_SOFTWARE (e.g. Apache/2.0.40 (Red Hat Linux))

system stuff:

TIME_YEAR

TIME_MON

TIME_DAY

TIME_HOUR

TIME_MIN

TIME_SEC

TIME_WDAY

TIME

specials:

API_VERSION

THE_REQUEST

REQUEST_URI (e.g. /test.php)

REQUEST_FILENAME

IS_SUBREQ

NOTA : You can match this list against a “phpinfo()” command if you are running a PHP-written site.

I’ve not had to try every variables. Here is the list of variables I’ve used so far :

HTTP_USER_AGENT

HTTP_REFERER

HTTP_HOST

REMOTE_ADDR

REMOTE_HOST

SCRIPT_FILENAME

So our RewriteCond directive will be some kind of:

RewriteCond %{HTTP_USER_AGENT} CondPattern Flag (optionnal)

RewriteCond %{HTTP_REFERER} CondPattern Flag (optionnal)

RewriteCond %{REMOTE_ADDR} CondPattern Flag (optionnal)

RewriteCond %{REMOTE_HOST} CondPattern Flag (optionnal)

RewriteCond %{SCRIPT_FILENAME} CondPattern Flag (optionnal)

Now, let’s see the CondPattern part of it. It’s a bit more complex, for you need to know what a “regular expresion” is. Well, if you do not, you gonna feel lonely. Read this page first :Using Regular Expressions, by Stephen Ramsay - Electronic Text Center - University of Virginia, and then, come back here. In the forthcoming pages, I’ll assume you do know about regular expressions. Your CondPattern can be any regular expression on the considered string.

For instance, to discriminate any user agent containing the string “Frontpage”:

RewriteCond %{HTTP_USER_AGENT} Frontpage

Flags will allow you to tweak the rewriteCond behaviour. For instance, to discriminate any user agent containing the string “Frontpage” without case sensibility, just set the [NC] flag (”NC” for “no case”):

RewriteCond %{HTTP_USER_AGENT} Frontpage [NC]

A flag is optionnal. Between two adjacent RewriteCond directives is an implicit logical AND. You will need the [OR] flag to set a logical OR. For instance, to discriminate any user agent containing the string “Frontpage” without case sensibility (”NC” = no case) AND any referer containing “foo”:

RewriteCond %{HTTP_USER_AGENT} Frontpage [NC]

RewriteCond %{HTTP_REFERER} foo

For instance, to discriminate any user agent containing the string “Frontpage” without case sensibility (”NC” = no case) OR any referer containing “foo”, add an OR flag separated by a comma:

RewriteCond %{HTTP_USER_AGENT} Frontpage [NC,OR]

RewriteCond %{HTTP_REFERER} foo

For instance, to discriminate any user agent containing the string “Frontpage” without case sensibility (”NC” = no case) OR any referer containing “foo” AND a “remote host” ending with “myprovider”:

RewriteCond %{HTTP_USER_AGENT} Frontpage [NC,OR]

RewriteCond %{HTTP_REFERER} foo [OR]

RewriteCond %{REMOTE_HOST} myprovider$

You can specify a non-matching pattern with a “!” sign before it. For instance, to discriminate any user agent containing the string “Frontpage” without case sensibility (”NC” = no case) OR any referer containing “foo” AND a “remote host” NOT ending with “myprovider”:

RewriteCond %{HTTP_USER_AGENT} Frontpage [NC,OR]

RewriteCond %{HTTP_REFERER} foo [OR]

RewriteCond %{REMOTE_HOST} !myprovider$

And so on…