Today I was playing (more) with mod_rewrite, and came to an interesting requirement: how to redirect a page that receives a specific parameter value to another URL (as in article.php?id=57 to article.php?id=686)?

Normally you would use mod_rewrite to make clean URLs or to hide parameters as part of the query string.  Now, the requirement that I had this time was to redirect a page that received an specific parameter (thru query string), to a different page.

All the mod_rewrite rules that I tried wouldn’t work, until I paired them with RewriteCond.  Here is the sample:

RewriteCond %{QUERY_STRING} '=id=138'

RewriteRule ^product\.php? product.php?id=33 [R=301,L]

What this will do:

1. Check if the query string is ‘id=138′  (note that we’re still not checking the file name receiving the parameter, we’re just checking the query string value).
2. Perform the actual redirection to product.php?id=33 if the requested page is product.php (with the previously matched condition of ‘id=138′).

I used this trick to redirect visitors from product # 138 to product # 33  (take a visitor from product.php?id=138 to product.php?id=33).