Simple Mod Rewrite?

[MrApples]

I need a rule that will send everything after the '.com/' to a PHP file. I've gotten close but I don't know how to get the variables to work for the original URL and not the URL I'm redirecting to.

http://www.domain.com/blah/blah/blah.html => /script.php?a=blah/blah/blah.html

Thank you in advance if anyone chooses to help.

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PS: Another related question

How would I check if a file exists with mod rewrite? I am also stuck on the variable part here.

RewriteCond %{DOCUMENT_ROOT}/wp-content/cache/supercache/%{HTTP_HOST}/$1/index.html -f
That line there does that, but I need it to work for a $1 equal to "^([^/\.]+)/?$"

Any help would be greatly appreciated. This is for caching.