Using Apache's mod rewrite how to redirect depending the query string?

Using Apache's mod rewrite how to redirect foo.php?r=ok to boo.php (that is, depending the query string: if r = ok the开发者_JAVA百科n redirect).

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you can't use query string (the string after "?" character) as variable for rewrite, because query string is not a part of URL path.

you need to modify foo.php?r=ok to some string path like "foo.php/redirect/"

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From the Apache manual discussing mod_rewrite:

If you wish to match against the hostname, port, or query string, use a RewriteCond with the %{HTTP_HOST}, %{SERVER_PORT}, or %{QUERY_STRING} variables respectively.

Look closely at RewriteRules and RewriteConditions

EDIT: Added a working example

The RegEx use to write these is just pure heaven </sarcasm>

Any how... here's a simple rule (Apache2, Mac OS X 10.5.8)

RewriteCond $1 ^(foo\.php)
RewriteCond %{QUERY_STRING} (r=ok) 
RewriteRule (foo\.php)      /bar.php [R]

I tested this for as many obvious caveats that I could think of (ie r=ko, oof.php, foo.php?r=o), but couldn't break it.