mod_rewrite QUERY_STRING value to new URL

Question

I've tried so many ways to do this for days now and STILL somehow gotten nowhere. Making me crazy. Seems like it ought to be relatively easy.... I need to rewrite traffic from an old app to a new one, but the format of the values passed is different.
This: http://oldapp.com/download.aspx?filename=FILE-01.pdf has to rewrite to this: https://NEWapp.com/this/that/FILE-01.pdf

So I have to pull the value out of the QUERY_STRING, which in this example is FILE-01.pdf, and incorporate it into the new URL. There is always only one name/value pair in QUERY_STRING and it is always "download.aspx?filename=".

Seems really straightforward, right? But I keep missing it. I have tried many, many variations of this:

RewriteEngine On
RewriteCond %{QUERY_STRING} filename=([\S\s]+)
RewriteRule ^(.*)$ https://NEWapp.com/this/that/$1 [R,L]

I'm working with IBM HTTP Server v8.0, which is basically Apache 2.2.

SOLUTION:

RewriteEngine On
RewriteCond %{QUERY_STRING} ^filename=([^&]+)
RewriteRule ^(.*)$ https://NEWapp.com/this/that/%1? [R,L]

Answer 1

Try:

RewriteEngine On
RewriteCond %{QUERY_STRING} filename=([^&]+)
RewriteRule ^download.aspx$ https://NEWapp.com/this/that/%1 [R,L]

When you access a capture group from a RewriteCond you need to use the backreference operator % rather than the $ prefix which would be used for capture groups in a RewriteRule

Answer 2

SOLUTION:

It really seems like arco444's excellent answer should have done this, but, this is what finally works:

RewriteEngine On
RewriteCond %{QUERY_STRING} ^filename=([^&]+)
RewriteRule ^(.*)$ https://NEWapp.com/this/that/%1? [R,L]

I don't understand why this works and a specific match on download.aspx doesn't, but I am glad to have a solution. Much gratitude to arco444 and Dekel.

Answer 3

Following arco444 I would add a question mark at the end to make sure the query string doesn't go to the end of the url as well.

RewriteEngine On
RewriteCond %{QUERY_STRING} ^filename=([^&]+)
RewriteRule ^download.aspx https://NEWapp.com/this/that/%1? [R,L]

If you would not add the question mark the final url will be https://NEWapp.com/this/that/FILENAME.ext?filename=FILENAME.ext