?url=sth/a to /sth/a

[blid]

Currently I can access specific site in two ways:

1. http://a.com/foo/bar
 2. http://a.com/index.php?url=foo/bar

What I'm trying to achive is to allow to do it only using first way, and make redirect 301 on the second to the first one. Here's the code which I made so far and put into .htaccess:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php?url=$1 [QSA,L]

#tricky part
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /index.php\?url=?(.*)\ HTTP/ RewriteRule ^index.php$ http://a.com/$1 [R=301,L]

Currently it do almost all the job, it's redirecting index.php to /, but index.php?url=foo/bar to /?url=foo/bar and I can't manage to make it right.
TIA.

[g1smd]

Don't forget to escape literal periods in patterns.

You'll need %1 not $1 as the correct backreference.

Clear the appended query string by adding a trailing question mark to the end of the redirect target URL.

Change the pattern

^index.php$

to

^(index\.php)?$

so that requests for

http://example.com/?url=foo/bar

are also redirected.

Technically, the "/" is not allowed in the parameters attached to a URL, so you might yet encounter other issues.

[blid]

@g1smd: Thank you for your answer.
I did the workaround in php, but I don't think it's "the right way" so I'm still struggling with it.
I followed your advice and now it looks like this:

RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /index\.php\?url=(.*)\ HTTP/ 
RewriteRule ^(index\.php)?$ http://example.com/%1? [R=301,L] 

It doesn't work for ?url=foo/bar .
I'd also like to index.php (with no parameters) be redirected 301 to example.com, is it even possible without writing new set of rules ?

[g1smd]

As far as I know the "/" will have to be encoded for this to work.

The "/" is not allowed in parameters.

[blid]

It's such a shame I can't edit my post, because obviously I forgot to mention that maybe ?url=foo/bar doesn't work but index.php?url=foo/bar works great.

[jdMorgan]

You need to make "index.php" optional in both lines...

RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /(index\.php)?\?url=(.*)\ HTTP/
RewriteRule ^(index\.php)?$ http://example.com/%1? [R=301,L]

Jim