There's a few other environmental variables to consider
re:search/execution paths, see table on p.182, pickaxe2:

RUBYLIB: additional search paths to be searched after $LOAD_PATH or $:
if $SAFE == 0

Also, note that rub does *not* add your current script's directory to
the execution path (like python does), so you'll often see something
like:

require File.dirname(__FILE__) + '/../moduleInArbitraryLocation'

see also RUBYPATH, RUBYLIB_PREFIX (win32).  Also note that you can't
make permanent changes to $PATH or other environmental vars on your win
or unix box by issuing command such as ENV['TERM']=whatever.  If you
write to ENV['TERM'], those changes are local to the process.