Last Updated: 2024-11-21

Say I want to hard-code that my program's output is to be paged via the more command. (i.e. do this in Ruby etc. instead of ad-hoc on the command line)

Then I need to:

• only take action if the program is connected to a tty. Why? Because there is no point in using a pager if you are feeding this program's output into another program that humans do not need to read (e.g. via a pipe)
• open a write pipe to the pager
• ensure the pipe gets closed by my process (not automatically by the OS) - otherwise the pager output goes over the shell prompt or disappears altogether.
• set $stdout to be the pipe, such that calling puts sends data to pager pipe

if $stdout.tty?
  # Take stock of this way of opening a write pipe!
  pager = open("|more", "w")
  # Be careful to close pipe
  at_exit { pager.close }
  $stdout = pager
end
puts text

Resources

• https://www.rubytapas.com/2017/06/26/episode-485-open-pipe/