request.env is a Ruby Array that contains information about a visiting user’s and server environments.
request.env is accessible on all pages hosted in a ruby on rails site. The Array contains the following key/value pairs:

• SERVER_NAME
• PATH_INFO
• REMOTE_HOST
• HTTP_ACCEPT_ENCODING
• HTTP_USER_AGENT
• SERVER_PROTOCOL
• HTTP_CACHE_CONTROL
• HTTP_ACCEPT_LANGUAGE
• HTTP_HOST
• REMOTE_ADDR
• SERVER_SOFTWARE
• HTTP_KEEP_ALIVE
• HTTP_REFERER
• HTTP_COOKIE
• HTTP_ACCEPT_CHARSET
• REQUEST_URI
• SERVER_PORT
• GATEWAY_INTERFACE
• QUERY_STRING
• REMOTE_USER
• HTTP_ACCEPT
• REQUEST_METHOD
• HTTP_CONNECTION

For testing purposes it might be useful to print out a table with the request.env information in it.

<% for item in request.env %>

<% end %>