wordpress - mod_rewrite replace query string key -

in short, i'm trying change given url:

http://mydomain.com/category/title/attachment/randomstring_?resolution=320x480 

with

http://mydomain.com/category/title/attachment/randomstring_320x480 

in essence, removing ?resolution= query string , adding value path.

the category, title, , randomstring values dynamic, placement should same.

i don't know if matters, being used in wordpress.

i tried following, 404:

<ifmodule mod_rewrite.c> rewriteengine on rewritebase /  rewritecond %{query_string} ^resolution=([0-9]{3,4}x[0-9]{3,4})$ rewriterule ^$ ${request_uri}%1/? [r]  rewriterule ^index\.php$ - [l] rewritecond %{request_filename} !-f rewritecond %{request_filename} !-d rewriterule . /index.php [l] </ifmodule> 

any appreciated ;)

well, after lot of trial , error (and reading rewritelog output), got working following:

<ifmodule mod_rewrite.c> rewriteengine on rewritebase / rewriterule ^index\.php$ - [l]  rewritecond %{query_string} ^resolution=(.*)$ rewriterule . %{request_uri}%1? [r=301,l]  rewritecond %{request_filename} !-f rewritecond %{request_filename} !-d rewriterule . /index.php [l] </ifmodule> 

the key issues original solution:

• using ^$ instead of . in rewriterule
• using /? instead of ? in rewriterule
• not including ,l in rewriterule flags

for curious, including ? in rewriterule prevents query_string remaining in request.