File to test how fish's redirection works

test.rb

require 'open3'

def show_printed_for(pipe_code)
  out, err, status = Open3.capture3 "fish", stdin_data: <<-PROGRAM
    ruby -e '
      $stdout.print "outmsg"
      $stderr.print "errmsg"
    ' #{pipe_code} ruby -e '
      print "PIPED(\#{$stdin.read})"
    '
  PROGRAM

  puts "OUT: #{out.inspect}"
  puts "ERR: #{err.inspect}"
  puts

  raise 'FAILED!' unless status.success?
end

puts "Normally, err in a pipeline goes to process's err"
show_printed_for "|"
# OUT: "PIPED(outmsg)"
# ERR: "errmsg"

puts "With `^|`, err goes to input of next in pipeline, and out goes to process's out"
show_printed_for "^|"
# OUT: "outmsgPIPED(errmsg)"
# ERR: ""

puts "With `2>&1`, both go to pipe"
show_printed_for "2>&1"
# OUT: "errmsgoutmsg"
# ERR: ""