ENV[ ‘REQUEST_URI’ ] = “/demo/index”

In the "Rails Way" book, the following was written in the console:

ENV[ ‘REQUEST_URI’ ] = “/demo/index”

I searched for a place to describe what ENV[ ‘REQUEST_URI’ ] means but
didn't find.

I know it is clear here. But, I want to know: Is ENV and 'REQUEST_URI']
predefined? In other words, do they act like methods I just reference
to?

Thanks.

In the "Rails Way" book, the following was written in the console:

ENV[ ‘REQUEST_URI’ ] = “/demo/index”

I searched for a place to describe what ENV[ ‘REQUEST_URI’ ] means but
didn't find.

I know it is clear here. But, I want to know: Is ENV and 'REQUEST_URI']
predefined? In other words, do they act like methods I just reference
to?

ENV is the hash of environment variables (it's not quite a hash if my
memory is correct). When using CGI web servers tell the application
about the request by setting a bunch of environment variables.

Fred

Thanks @Fred.