popen3

Open stdin, stdout, and stderr streams and start external executable. In addition, a thread for waiting the started process is noticed. The thread has a pid method and thread variable :pid which is the pid of the started process.

Block form:

Open3.popen3([env,] cmd... [, opts]) {|stdin, stdout, stderr, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  ...
  exit_status = wait_thr.value # Process::Status object returned.
}

Non-block form:

stdin, stdout, stderr, wait_thr = Open3.popen3([env,] cmd... [, opts])
pid = wait_thr[:pid]  # pid of the started process.
...
stdin.close  # stdin, stdout and stderr should be closed explicitly in this form.
stdout.close
stderr.close
exit_status = wait_thr.value  # Process::Status object returned.

The parameters cmd... is passed to Process.spawn. So a commandline string and list of argument strings can be accepted as follows.

Open3.popen3("echo a") {|i, o, e, t| ... }
Open3.popen3("echo", "a") {|i, o, e, t| ... }
Open3.popen3(["echo", "argv0"], "a") {|i, o, e, t| ... }

If the last parameter, opts, is a Hash, it is recognized as an option for Process.spawn.

Open3.popen3("pwd", :chdir=>"/") {|i,o,e,t|
  p o.read.chomp #=> "/"
}

wait_thr.value waits the termination of the process. The block form also waits the process when it returns.

Closing stdin, stdout and stderr does not wait the process.

# File lib/open3.rb, line 73
  def popen3(*cmd, &block)
    if Hash === cmd.last
      opts = cmd.pop.dup
    else
      opts = {}
    end

    in_r, in_w = IO.pipe
    opts[:in] = in_r
    in_w.sync = true

    out_r, out_w = IO.pipe
    opts[:out] = out_w

    err_r, err_w = IO.pipe
    opts[:err] = err_w

    popen_run(cmd, opts, [in_r, out_w, err_w], [in_w, out_r, err_r], &block)
  end