code: function build_shell(fields) {
  	var $fields = Array.isArray(fields) ? normalizeFields(fields) : ['ProcessId','Name','Path','ParentProcessId','Priority'];
  	
  	var args = command.shell_arg.split(' ');
  	args.push(`${command.ps} | ${command.select} ${ $fields.join(',') } | ${command.convert}`);
  
  	return shell(command.shell, args);
  }
docs: Build shell command
  @param  {Array} fields
  @return {Object}        child_process instance