code: protected String getFileName(LineParser lp){
  		String fileName = lp.getArgs();
  		if(fileName==null){
  			fileName = this.lastScript;
  		}
  		else if(!fileName.endsWith("." + SCRIPT_FILE_EXTENSION)){
  			fileName += "." + SCRIPT_FILE_EXTENSION;
  		}
  		return fileName;
  	}
docs: Returns a file name taken as argument from the line parser with fixed extension
  @param lp line parser
  @return file name, null if none found