Where is my file?

I have a file whose name is

  f:\Ralph-Rails-Apps\myproject\public\documentation\marketing\myproject-Upgrade-and-Update-Policy.htm

on my Windows machine

I have attempted to open this file (which I know exists) in my
controller using a variety of names to no avail.
  /public/documentation/marketing/myproject-Upgrade-and-Update-Policy.htm
  public/documentation/marketing/myproject-Upgrade-and-Update-Policy.htm
  /documentation/marketing/myproject-Upgrade-and-Update-Policy.htm
  documentation/marketing/myproject-Upgrade-and-Update-Policy.htm

How can I open this file in both my development environment (Windows &
webrick) and on my server (Linux abd Apache(?))

Try
"#{Rails.root}/public/documentation/marketing/myproject-Upgrade-and-Update-Policy.htm"

or

"#{RAILS_ROOT}/public/documentation/marketing/myproject-Upgrade-and-Update-Policy.htm"

What do you mean by 'open this file in my controller'? Show us some code.

If you are trying to view it in a browser or redirect to it, it would
be the third one (/documentation/....).

Colin

“#{RAILS_ROOT}/public/documentation/marketing/myproject-Upgrade-and-Update-Policy.htm”