text: /**
   * Validate shell command
   */
  module.exports.isValidShellCommand = (command) => {
  
      // Invalid if it command is an empty string.
      if(!command) {
          return false;
      }
  
      const allowedCommands = ['cd','ls','clear','ll','l','git','npm'];
  
      /**
       * Do not allow command chaining
       */
      const regex = /[;&|$()<>]/gm;
  
      if(regex.test(command)) {
          return false;
      }
  
      commands = command.toLowerCase().split(' ');
  
      // Compare first word of command with alloweded command list (eg. cd /home => compare "cd" with allowed commands)
      return (allowedCommands.indexOf(commands[0]) > -1);
  }