Open3 grants you access to stdin, stdout, and stderr when running another program. Example:

require "open3"
include Open3

stdin, stdout, stderr = popen3('nroff -man')

Open3.popen3 can also take a block which will receive stdin, stdout and stderr as parameters. This ensures stdin, stdout and stderr are closed once the block exits. Example:

require "open3"

Open3.popen3('nroff -man') { |stdin, stdout, stderr| ... }