Stream and capture subprocess stdout

shell.rb

require 'open3'

def subprocess(*cmd)
  Open3.popen3(*cmd) {|i,o,e,t|
  
    out = Thread.new do
      o.each_with_object([]) do |line,memo| 
        memo << line
        yield line if block_given?
      end.join
    end
    
    err = Thread.new {e.read}
    
    i.close
    
    [out.value, err.value, t.value]
  }
end

p subprocess('man', 'ls') {|l| p l}