io.open (filename [,mode])

This function opens a file,in the mode specified in the string mode. It returns a new file handle,or,in case of errors,nil plus an error message.

使用函数返回的第二个值的示例用法如下：

local f,err = io.open("filename.txt","w")
if f then
    -- do something with f
else
    print("Error opening file: " .. err)
end

例如,如果进程没有打开文件的权限,则会打印出以下消息：

Error opening file: filename.txt: Permission denied