require 'rbconfig'
 
$stdout.sync = true
 
def hello(source, expect_input)
  puts "[child] Hello from #{source}"
  if expect_input
    puts "[child] Standard input contains: \"#{$stdin.readline.chomp}\""
  else
    puts "[child] No stdin, or stdin is same as parent's"
  end
  $stderr.puts "[child] Hello, standard error"
end
 
THIS_FILE = File.expand_path(__FILE__)
 
RUBY = File.join(Config::CONFIG['bindir'], Config::CONFIG['ruby_install_name'])
 
if $PROGRAM_NAME == __FILE__
  puts "1. Backtick operator"
  output = `#{RUBY} -r#{THIS_FILE} -e'hello("backticks", false)'`
  output.split("\n").each do |line|
    puts "[parent] output: #{line}"
  end
  puts
 
  puts "2. Kernel#system"
  success = system(RUBY, "-r", THIS_FILE, "-e", 'hello("system()", false)')
  puts "[parent] success: #{success}"
  puts
 
  puts "3. Kernel#fork"
  pid = fork do
    hello("fork()", false)
  end
  Process.wait(pid)
  puts "[parent] pid: #{pid}"
  puts
end