Question

Is there a way to run a ruby script and while executing commands in the script ,still respond to key stroke ?

I want to run a ruby script but be able to press “Space” and pause the script (after currently running command executes ), and then press “Space” again and resume the script .

My only idea (and im sure its a weird one) , is to open a new thread and wait for key strokes there ,
then when ill get a key stroke , set a stop_flag.
Only now it looks like i need to be checking this flag after each command to know when to stop.

Answer 1

You can use a signal to turn debug output on and off at will, if you have a logger set up with appropriate code sprinkled throughout your script:

 pid = fork do

  # set up a logger
  require 'logger'
  log = Logger.new(STDOUT)
  log.level = Logger::INFO

  # toggle between INFO and DEBUG log levels on SIGUSR1
  trap(:SIGUSR1) do
    if log.level == Logger::DEBUG
      log.level = Logger::INFO
    else
      log.level = Logger::DEBUG
    end
  end

  # Main loop - increment a counter and occasionally print progress
  # as INFO level.  DEBUG level prints progress at every iteration.
  counter = 0
  loop do
    counter += 1
    exit if counter > 100
    log.debug "Counter is #{counter}"
    log.info "Counter is #{counter}" if counter % 10 == 0
    sleep 0.1
  end

end

# This makes sure that the signal sender process exits when the
# child process exits - only needed here to make the example
# terminate nicely.
trap(:SIGCLD) do
  exit(0) if Process.wait(-1, Process::WNOHANG) == pid
end

# This is an example of sending a signal to another process.
# Any process may signal another by pid.
# This example uses a forking parent-child model because this
# approach conveniently yields the child pid to the parent.
loop do
  puts "Press ENTER to send SIGUSR1 to child"
  STDIN.gets
  Process.kill :SIGUSR1, pid
end

The forking and SIGCLD trapping is to make the example fit into one file; any process may send a signal to another.

The code inside the fork block is your script. The script sets up a logger with a default log level of INFO, and a handler for the SIGUSR1 signal that toggles the logger between DEBUG and INFO levels.

The stuff outside of the fork block is just an example of sending a signal to another process. Pressing ENTER will send the signal and alter the logging level of the other process.

This works on POSIX systems, I have no idea about Windows.