In what language are the Nginx and Apache configuration files written?

In what language are the Nginx and Apache configuration files written?
I recently saw an example of a Nginx configuration file rewriting using a variable starting with $.
Perl or PHP?

This is because I wanted to change the HTTP header dynamically (the UNIX time is a dynamic element), so I was wondering what to do, but there was an example of setting the condition document in the configuration file, so I think I could use it as a reference.
(It would be helpful if there were other things that could be done in this way.)

Thank you for your cooperation.