Htaccess RewriteCond based on environment variable

Question

I find apache very unfriendly.

Anyway. I have this:

RewriteRule (.*) - [QSA,E=DOMAIN_NAME:localhost.com]

This doesn't redirect, which is fine:

RewriteCond "www.%{ENV:DOMAIN_NAME}" "!=www.localhost.com"
RewriteRule ^ https://%{HTTP_HOST}?err=%{ENV:DOMAIN_NAME} [L,R=301]

This doesn't redirect, which is fine:

RewriteCond "%{HTTP_HOST}" "!=www.localhost.com"
RewriteRule ^ https://%{HTTP_HOST}?err=%{ENV:DOMAIN_NAME} [L,R=301]

This does redirect:

RewriteCond "www.%{ENV:DOMAIN_NAME}" "!=%{HTTP_HOST}"
RewriteRule ^ https://%{HTTP_HOST}?err=%{ENV:DOMAIN_NAME} [L,R=301]

Is very frustrating. I'm stuck in checking two variables if they match...

Answer 1

This does redirect:

RewriteCond "www.%{ENV:DOMAIN_NAME}" "!=%{HTTP_HOST}"

Because server variables of the form %{VARNAME} are not expanded in the CondPattern (2nd argument to the RewriteCond directive). You are comparing against the literal string "%{HTTP_HOST}", which is obviously different to "www.localhost.com", so the condition is successful.

You need to use a regex with an internal backreference instead. For example:

RewriteCond www.%{ENV:DOMAIN_NAME}@%{HTTP_HOST} !^([\w.]+)@\1$

Where @ is just an arbitrary character that does not occur elsewhere in the string being checked. And \1 is a backreference to the captured subpattern, ie. ([\w.]+).

Or use an Apache Expression (Apache 2.4):

RewriteCond expr "'local.%{ENV:DOMAIN_NAME}' != %{HTTP_HOST}"

Aside:

RewriteRule (.*) - [QSA,E=DOMAIN_NAME:localhost.com]

If you are simply setting an env var then you don't need to capture (or even match) the entire URL-path and the QSA flag is superfluous (since there is no substitution). For example:

RewriteRule ^ - [E=DOMAIN_NAME:localhost.com]