Example of a pseudo-terminal shell via PTY

shellout.rb

require 'pty'
require 'expect'

def shellout(shell, *lines)
  prompt = /^(?:#{Regexp.escape(ENV['PS1'])}|#{Regexp.escape(ENV['PS2'])})/
  lines << 'exit'

  PTY.spawn(shell) do |stdin,stdout,pid|
    begin
      lines.each do |line|
        buffer, match = stdin.expect(prompt)
        print(buffer || "\n")
        stdout.puts line
      end
    rescue Errno::EIO
      # the presence of this rescue indicates my not knowing how to detect
      # that stdout can no longer accept inputs. I think that after the exit
      # 2, the slave no longer is available, so while stdout is still open,
      # there isn't anything to recieve the data and hence the error.
      #
      # the unfortunate symptom of this rescue is the prompt being printed one
      # last time (since print buffer is ok before stdout fails)
    end

    print stdin.read
    Process.wait(pid)
  end
end

ENV['PS1'] = '$ '
ENV['PS2'] = '> '

# single command
shellout 'sh', 
'echo a'
puts "status: #{$?.exitstatus}"
puts

# multiple commands + context
shellout 'sh', 
'A="B"',
"echo a",
"echo $A"
puts "status: #{$?.exitstatus}"
puts

# multiline command, redirections
shellout 'sh', 
"cat > stdout <<DOC",
"abc",
"xyz",
"DOC",
"cat stdout"
puts "status: #{$?.exitstatus}"
puts

# exit and flow control
shellout 'sh', 
"if false",
"then exit 0",
"fi",
"if true",
"then exit 2",
"fi"
puts "status: #{$?.exitstatus}"
puts

# fancy output
shellout 'sh', 
"ruby <<'SCRIPT'",
'print "?";  $stdout.flush; sleep 1',
'print "\r"; $stdout.flush',
'print ".";  $stdout.flush',
"puts",
"SCRIPT"
puts "status: #{$?.exitstatus}"
puts