def shell_output
      $shell_history ||= []
      cmd = get_string("Enter shell command:", :maxlen => 50) do |f|
        require 'canis/core/include/rhistory'
        f.extend(FieldHistory)
        f.history($shell_history)
      end
      if cmd && !cmd.empty?
        run_command cmd
        $shell_history.push(cmd) unless $shell_history.include? cmd
      end
    end
def shell_output
      $shell_history ||= []
      cmd = get_string("Enter shell command:", :maxlen => 50) do |f|
        require 'canis/core/include/rhistory'
        f.extend(FieldHistory)
        f.history($shell_history)
      end
      if cmd && !cmd.empty?
        run_command cmd
        $shell_history.push(cmd) unless $shell_history.include? cmd
      end
    end
prompts user for unix command and displays output in viewer