EM::SystemCommand

EM::SystemCommand is an popen3 abstraction for eventmachine to easily create subprocesses with eventmachine. The goal is to provide an easy way to invoke system commands and to read and handle their outputs. When creating an EM::SystemCommand object its basically like a popen. It has #stdin, #stdout and #stderr. Which are related to EM::Connection.

Installation

Add this line to your application's Gemfile:

gem 'em-systemcommand'

And then execute:

$ bundle

Or install it yourself as:

$ gem install em-systemcommand

Usage

To simply run a process you can instatiate an EM::SystemCommand object and set up the callbacks in the yielded block.

EM.run do
  EM::SystemCommand.execute 'my_command' do |on|
    on.success do |ps|
      puts "Success!"
    end
    
    on.failure do |ps|
      puts "Failure with status #{ps.status.exitstatus}"
    end
  end
end

When you want to retreive output, you can use the methods #update, #line and #data on a pipe object like so:

EM.run do
  EM::SystemCommand.execute 'my_command' do |on|
    on.success do |ps|
      puts "Success!"
    end
    
    on.stdout.data do |data|
      puts "Data: #{data}"
    end
    
    on.stdout.line do |line|
      puts "Line: #{line}"
    end
    
    # `#output` gets the whole output buffer.
    # This means, it has theoretically the screen you´d get when
    # invoking the command in the shell. Although only \r is used.
    on.stdout.update do |output|
      puts output
    end
  end
end

Pipe objects even have a nice convenient method #match which lets you match output against a regular expression:

EM.run do
  EM::SystemCommand.execute 'echo "25%\n"; sleep 1; echo "50%\n"; sleep 1; echo "75%\n"; sleep 1; echo "100%\n"; exit 0;' do |on|
    on.success do |ps|
      puts "Success!"
    end
    .
    on.stdout.match /([0-9]+)%/, in: :line do |match, progress|
      puts "Percentage: #{progress}"
    end
  end
end

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request