gistfile1

    # fork + exec(arg, *args)
    # the stdfd argument may be used to use an existing IO object (with an
    # associated fd) instead of new pipes for stdin/stdout/stderr, no other fds
    # will be open in the child
    # returns [pid, stdin, stdout, stderr]
    # fd 3 through NOFILE are closed before exec
    def popen(stdfd, arg, *args)
        parent = []
        child = []
        # create pipes for stdin/stdout/stderr or use objects from stdfd
        0.upto(2) do |i|
            if stdfd[i]
                parent[i], child[i] = stdfd[i], stdfd[i]
            elsif i == 0
                child[0], parent[0] = IO.pipe
            else
                parent[i], child[i] = IO.pipe
            end
        end
        pid = Kernel.fork do
            STDIN.reopen(child[0])
            STDOUT.reopen(child[1])
            STDERR.reopen(child[2])
            # (try) to close all non-standard fds
            3.upto(NOFILE) do |i|
                begin
                    IO.new(i).close
                rescue
                end
            end
            begin
                Kernel.exec(arg, *args)
            rescue Exception => e
                $stderr.puts e.message
            ensure
                Kernel.exit!(127)
            end
        end
        # close pipes of client
        0.upto(2) do |i|
            begin
                child[i].close if parent[i].fileno != child[i].fileno
            rescue
            end
        end
        return [pid]+parent
    end