[SOLVED] Capturing STDOUT from a forked process

Capturing STDOUT from a forked process

I want to fork a process, wait for the child process to finish, then get the STDOUT from the child process. Here's code that doesn't work:

require 'stringio'

hold_stdout = $stdout
results = $stdout = StringIO.new

if pid = fork()
  Process.wait(pid)
else
  $stdout = hold_stdout
  puts 'stuff in child process'
  exit
end

$stdout = hold_stdout
puts 'results from child:'
puts results.string

That gives this output:

stuff in child process
results from child:

Not sure what to do here. If you ask me "why are you...?" the answer is because I don't know what I'm doing. Any help appreciated.

Solution

You can use pipes and redirect the stdout in the child process.

reader, writer = IO.pipe

if pid = fork()
  writer.close
  Process.wait(pid)
else
  reader.close
  $stdout.reopen(writer)
  puts 'stuff in child process'
  exit
end

puts 'results from child:'
puts reader.read

This should print out what you want.