mod_rewrite and double slash issue

RewriteRule ^\/?(.*)$ http://www.example.com/$1 [R=301,L]

Putting a slash into your pattern should resolve this issue:

RewriteRule ^/(.*)$ http://www.example.com/$1 [R=301,L]

Actually, you will always have double slashes due to

RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]

combined with the fact that REQUEST_URI (that you are matching on) normally contains a starting slash. What you can try is RewriteRule ^(.*)$ http://example.com$1, and then send a broken HTTP request GET foo HTTP/1.0 and see if Apache deals with it properly.

Fixed with:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com$1 [R=301,L]

because $1 by default contains the index path /