Session::* offers a set of classes built upon Open3::popen3 for driving
external progams via pipes.  It offers a significant abstraction over
Open3::popen in that the stdout/stderr of each command sent can be deliniated:


      i,o,e = Open3::popen3 '/bin/sh'

      i.puts 'ls'
      i.puts 'echo 42'

  now, how to determine the boundry between the output from 'ls' and 'echo'?
  the only (simple) way is start a process for each command

      i,o,e = Open3::popen3 '/bin/sh'
      i.puts 'ls'
      stdout, stderr = o.read, e.read

      i,o,e = Open3::popen3 '/bin/sh'
      i.puts 'echo 42'
      stdout, stderr = o.read, e.read


    sh = Session::new

    stdout, stderr = sh.execute 'ls'
    stdout, stderr = sh.execute 'echo 42'

Both stderr and stdout can be redirected, and the exit_status of each command
is made available:

    bash = Session::Bash.new
    stdout, stderr = StringIO::new, StringIO::new

    bash.execute 'ls', :stdout => stdout, :stderr => stderr
    # bash.execute 'ls', 1 => stdout, 2 => stderr           # same thing
    # bash.execute 'ls', :o => stdout, :e => stderr         # same thing

    exit_status = bash.exit_status

A block form can be used to specify a callback to be invoked whenever output
has become availible:

  bash = Session::Bash.new

  bash.execute( 'long_running_command.exe' ) do |out, err|
    logger << out if out
    elogger << err if err

Sessions are Thread safe (in the sense that they do not block on io
operations) allowing commands spawned from guis to update widgets with output
while running in the background.

  button.configure 'action' => lambda do
    sh = Session::new
    sh.execute(cmd) do |o,e|
      out_widget.update o if o
      err_widget.update e if e


see samples/*


  - patches from @headius

  - move to github

  - added ability to specify stdin for Session::Bash and Session::Sh

      sh = Session::new

      sh.execute 'cat', :stdin => io
      sh.execute 'cat', :stdin => string
      sh.execute 'cat', :stdin => stringio

  - fixed warning of @debug being un-initialized

  - added a private munged version of Open3::open3.  the builtin one causes
    the child process to become a child of init, this was very inconvenient
    because it was sometimes hard to crawl proces trees - the parent was lost.
    now the seesion is a child process that has been detached using
    Process::detach.  this results in less suprising behaviour; for instance
    sending signal TERM to a process results in any sessions it had open dying
    as well.  you can use Session::use_open3=true or
    ENV['SESSION_USE_OPEN3']='1' for the old behaviour if you need it.
  - added Session::Bash::Login class.  this class opens a session which has
    all the normal settings of a bash loging shell (.bashrc is sourced).  this
    if often convenient as paths, aliases, etc. are set as normal.
  - moved the Spawn module inside the Session module.  now the Session module
    is the namespace for everything so using session pollutes namespace less.

  - fixed bug where setting track history after creation caused later failure in
    execute (@history =[] only in ctor).  thanks leon breedt
    <[email protected]>!
  - updates to README
  - included session-x.x.x.rpa file - thanks batsman <[email protected]>
  - to_str/to_s/to_yaml for History/Command is now valid yaml (updated samples
    to reflect this)
  - inspect for History/Command is now ruby's default 

  - greatly simplified read loop using two reader threads, one for stderr and
    one for stdout alongside a mutex to protect data.  this streamlined the code
    alot vs. the old select method including allowing removal of the linbuffer
    class.  the interface remains exactly as before however.

  - improved thread safe non-blocking read method
  - gemspec 

  - wrapped send_command in a Thread (send async) so output processing can
    commend immeadiately.  this was o.k. before, but had strange behaviour when
    using popen3 from threads.  thanks to tanaka akira for this suggestion.
  - iff ENV['SESSION_USE_SPAWN'] is set Session uses Spawn::spawn instead of
    Open3::popen3.  also noted that spawn seems to be a bit faster.
  - added tests for threads.
  - run 'sh SESSION_USE_SPAWN=1 ruby test/session.rb' to test using spawn
  - added test for idl so it's test is not run if system doesn't have it, all
    that should be required for 'ruby test/session.rb' is should be sh'
  - removed sample/tcsh and note about Tcsh and Csh in README - stderr
    redirection/separation is flaky in those shells

  - added Session.use_spawn=, AbstractSession.use_spawn=, and an :use_session=>
    option to AbstractSession#initialize.  if any of them are set the code uses
    Spawn::spawn to create external processes instead of Open3::popen3.
    Spawn::spawn uses named pipes (fifos) for IPC instead of forking and pipes.
    the fork used in popen3 can cause strange behaviour with multi-threaded apps
    (like a tk app).  see source for details

  - added Thread.exclusive{} wrapper when io is read to works in multi
    threaded apps