Sets up a pager program to pass output through. Tries the RI_PAGER and
PAGER environment variables followed by pager, less then more.
# File lib/rdoc/ri/driver.rb, line 1151
def setup_pager
return if @use_stdout
pagers = [ENV['RI_PAGER'], ENV['PAGER'], 'pager', 'less', 'more']
pagers.compact.uniq.each do |pager|
next unless pager
pager_cmd = pager.split.first
next unless in_path? pager_cmd
io = IO.popen(pager, 'w') rescue next
next if $? and $?.exited? # pager didn't work
@paging = true
return io
end
@use_stdout = true
nil
end