Reference capture groups of multiple RewriteCond in RewriteRule - .htaccess

Question

When I have multiple RewriteCond chained together, only the capture groups of the last RewriteCond can be referenced with %0-%9.
In the following problem the parameters in the query string of the url can be in any order. To parse them into a fancy url I would need to match each parameter in the query string individually:
RewriteCond %{QUERY_STRING} param1=([^&]+)
RewriteCond %{QUERY_STRING} param2=([^&]+)
RewriteCond %{QUERY_STRING} param3=([^&]+)
RewriteRule ^foo$ bar/%1/%2/%3/ [R]
Like I pointed out... this doesn't work. To fix this, I could reference the capture group of the previous RewriteCond in the next RewriteCond and 'propagate' each parameter to the actual RewriteRule:
RewriteCond %{QUERY_STRING} param1=([^&]+)
RewriteCond %1&%{QUERY_STRING} ^([^&]*)&.*param2=([^&]+)
RewriteCond %1&%2&%{QUERY_STRING} ^([^&]*)&([^&]*)&.*param3=([^&]+)
RewriteRule ^foo$ bar/%1/%2/%3/ [R]
This should work, but for each additional parameter it get's messier. An other solution could possibly be parsing one parameter and redirecting the client after each parameter (resulting in a lengthy chain of redirects, which I would like to avoid).
Is there an cleaner way of accessing the capture groups of all RewriteCond's in the RewriteRule (e.g. is it possible to name them or assign them to a variable so I can reference them somewhere else?)

Answer 1

You could try constructing the target URL inside the rewrite conditions:
RewriteCond ##%{QUERY_STRING} (.*)##(|.*&)param1=([^&]+)
RewriteCond %1/%3##%{QUERY_STRING} (.*)##(|.*&)param2=([^&]+)
RewriteCond %1/%3##%{QUERY_STRING} (.*)##(|.*&)param3=([^&]+)
RewriteCond %1/%3##%{QUERY_STRING} (.*)##(|.*&)param4=([^&]+)
RewriteCond %1/%3##%{QUERY_STRING} (.*)##(|.*&)param5=([^&]+)
RewriteCond %1/%3##%{QUERY_STRING} (.*)##(|.*&)param6=([^&]+)
RewriteRule ^foo$ /bar%1/%3? [L,R]
When I try to request:
/foo?param1=a&param2=b&param6=3&param3=4&param5=5&param4=6
I get redirected to:
/bar/a/b/4/6/5/3
Adding any additional required query string parameters won't make it look any more messy than it already is.

Answer 2

After experimenting some more, it would be possible to parse all parameters as environment variables and use them like that. I doubt it is very efficient though and I think any use-case that would need such a construction would be better of using a php page router. For fancy url's Jon Lin's solution would probably work better. It does however sort-of mimic what I had in mind.
I'll, however, put the code in here for demonstration:
#Parse all query key-value pairs to an environment variable with the q- prefix
RewriteCond %{QUERY_STRING} ^([^=]*)=([^&]*)(&(.*)|$)$
RewriteRule ^(.*)$ $1?%4 [E=q-%1:%2,N]
#If 'param1' existed in the query string...
RewriteCond %{ENV:q-param1} !^$
RewriteRule ^foo$ bar/%{ENV:q-param1} [END]
or even...
#Keep the original query string
RewriteCond %{ENV:qstring} ^$
RewriteCond %{QUERY_STRING} ^(.*)$
RewriteRule .* - [E=qstring:#%1]
#parse the query parameters to environment variables
RewriteCond %{ENV:qstring} ^#([^=]*)=([^&]*)(&(.*)|$)$
RewriteRule ^(.*)$ - [E=q-%1:%2,E=qstring:#%4,N]
#See that the original query string is still intact
RewriteCond %{ENV:q-param1} !^$
RewriteRule ^foo$ bar/%{ENV:q-param1} [QSA]