RewriteRule for multiple robots.txt

Question

I have a site with multiple domains and i need a robots.txt for each domain.

For example:

example.com will have robots-com.txt
example.se will have robots-org.txt
example.co.uk will have robots-co.uk.txt

etc... And the URL would be example.com/robots.txt

So I wrote this:

RewriteRule ^.*example\.(.*)/robots\.txt robots-$1.txt [L]

(i thought) that it would take the domain and add it to the end of the robots file. But it doesn't work.

How should I do, is it possible?

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I rewrote it like this, still doesn't work:

RewriteCond %{HTTP-HOST} ^.*example\.(.*)$
RewriteRule ^robots\.txt$ robots-%1\.txt [L]

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Working solution::

RewriteCond %{HTTP_HOST} ^.*example\.(.*)$
RewriteRule ^robots\.txt$ /robots-%1\.txt [L]