Using custom environment variables in .htaccess

I need something like this:

SetEnv foo bar.baz
RewriteEngine On

RewriteCond %{HTTP_HOST}开发者_开发问答 ^%{foo}$
RewriteRule ^(.*)$ http://www.foo/$1 [L]

UPD:

I have made as follows:

SetEnv HOSTNAME_ENV testsite
RewriteEngine On
RewriteCond %{HTTP_HOST} ^%{ENV:HOSTNAME_ENV}
RewriteRule ^(.*)$ http://www.%{ENV:HOSTNAME_ENV}/$1 [L,R=301]

But it doesn't work. %{ENV:HOSTNAME_ENV} is not defined.

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This won't work, because mod_rewrite does not expand variables in test patterns. Consequently, your expression will attempt to match the regular expression ^%{foo}$, not ^value_of_foo$.

Additionally, the documentation for SetEnv also makes a special note about order-of-processing in relationship to mod_rewrite. This actually does come into play here, despite the rules being applied later in the request handling than the scenario they're describing there. If you don't perform a rewrite that causes an internal redirection before testing against the environment variable you set, it will be blank.

Assuming you set the variable correctly, a potential workaround is to do this, although I feel like it isn't foolproof:

RewriteCond %{HTTP_HOST}#%{ENV:foo} ^([^#]+)#\1$

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Just set the environment using rewrite rules:

RewriteRule (.*) $1 [E=HOSTNAME_ENV:whatever.com]

This has also the advantage, that you are able to use RewriteCond.