Update: see the comment below from Alan Orth about how to implement this in a much cleaner way now!
When rewriting URLs in Apache through mod_rewrite, you have the possibility of using RewriteCond to only apply rewrites if the original resource has been called with a particular argument in the URL (such as “/file?oid=..”).
The solution in nginx was however a bit different, but thanks to Rewriting URL-params in nginx I got on the right track from the start.
In nginx this information is available through the $args variable, which will contain the complete query string. In Will’s example above he’ll replace the query string, but I were interested in inserting a specific parameter instead (and include the previous query string, so I couldn’t just do the “set $args ..” that he does in the example).
My first try was to simply use $1 in the rewrite destination, but this didn’t work – as rewrite will reset the captured patterns from the previous regular expression (since the rewrite source also is a regular expression). But by introducing my own, temporary variable I were able to save the value from the matching regular expression (for the GET parameter) and use it in my rewrite destination.
The following example shows how I ended up solving the issue. This will rewrite the URL only if the “oid” parameter is found at the beginning of the query string when the URL is requested, and the location = /oldURL limits the rewrite to requests for the old resource.
location = /oldURL {
if ($args ~ "^oid=(\d+)") {
set $key1 $1;
rewrite ^.*$ /newURL?param1=foo¶m2=bar&key1=$key1 last;
}
}
This will rewrite a request for /oldURL?oid=123&what=cheese to /newURL?param1=foo¶m2=bar&key1=123&oid=123&what=cheese — if you want to exclude the previous arguments, you can either just set $args directly to key1=$1 and just use param1=foo and param2=bar in the rewrite destination:
set $args key1=$1;
rewrite ^.*$ /newURL?param1=foo¶m2=bar last;
This might be cleaner, depending on what you’re trying to do.