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Apache RewriteRule and query strings

by Simon. Average Reading Time: about 2 minutes.

At first glance, the way the Apache mod_rewrite module handles query strings can be a little intimidating. mod_rewrite works by sitting on your server in a file called htaccess, and “catching” requests for URL‘s. It then checks these URL request against a series of rules and conditions you have set. If the request meets any of the rules and conditions, it applies then necessary changes to the URL, then reprocesses the request with the changes you have directed. Apache helpfully provides some RewriteCond documentation

The most common mistake people make when thinking of URL redirection with mod_rewrite, is they believe it creates something, or changes something. It doesn’t.

Here is a simple example, redirecting a page dependent upon its query string. The rewrite condition and rule looks like this:

RewriteCond %{QUERY_STRING} ^id=([0-9]*)$
RewriteRule ^page\.php$ http://www.example.com/page/%1.php [R=302,L]

The rewrite condition matches a numerical ID between 0 and 9. According to the official documentation, you would expect the following behaviour:

/page.php?id=1 -> http://www.example.com/page/1.php
/page.php?id=10 -> http://www.example.com/page/10.php

However, if you don’t append something new, then the original query is passed through by default. This results in the following:

/page.php?id=1 -> http://www.example.com/page/1.php?id=1
/page.php?id=10 -> http://www.example.com/page/10.php?id=10

If you want to discard the original query string you must append an empty question mark at the end of the rule; the query string not append or query string discard flag.

RewriteCond %{QUERY_STRING} ^id=([0-9]*)$
RewriteRule ^page\.php$ http://www.example.com/page/%1.php? [R=302,L]

Putting it all together, here’s a quick reference for dealing with query string in a RewriteRule.

Keep original query (i.e., the default behaviour)

RewriteRule ^page\.php$ /target.php [L]
# from http://www.example.com/page.php?foo=bar
# to http://www.example.com/target.php?foo=bar

Discard original query

RewriteRule ^page\.php$ /target.php? [L]
# from http://www.example.com/page.php?foo=bar
# to http://www.example.com/target.php

Replace original query

RewriteRule ^page\.php$ /target.php?bar=baz [L]
# from http://www.example.com/page.php?foo=bar
# to http://www.example.com/target.php?bar=foo

Append new query to original query

RewriteRule ^page\.php$ /target.php?bar=baz [QSA,L]
# from http://www.example.com/page.php?foo=bar
# to http://www.example.com/target.php?foo=bar&bar=foo

Dave Child has created a great mod_rewrite cheat sheet; a one-page reference sheet, listing flags for the RewriteRule and RewriteCond directives, list of server variables, a regular expression guide and several examples of common rules.

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