> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/4.3-bsd-unix-cao-zuo-xi-tong-she-ji-yu-shi-xian/di-yi-bu-fen-gai-lan/2.9.-zhong-duan.md).

# 2.9 终端

终端支持标准的系统 I/O 操作，也支持一组终端专用的操作，用来控制输入字符的编辑和输出延迟。最低层是控制硬件终端端口的终端设备驱动。终端输入按底层通信特性（如波特率）和一组软件可控参数（如奇偶校验）处理。

在终端设备驱动之上是行规程（line discipline），提供不同程度的字符处理。端口用于交互登录时，通常采用默认行规程。默认行规程有三种模式：原始（raw）、cbreak 和规范（cooked）。原始模式下，输入不加解释、立即传给读进程。cbreak 模式下，终端处理程序只解释那些引发信号或输出流控制的输入字符；其余字符同原始模式一样直接传给进程。规范模式下，输入经过处理提供标准的面向行的编辑功能，并按行呈现给进程。

输出方面，终端处理程序提供一些简单的格式化服务，包括：

* 把换行字符转换为“回车-换行”两字符序列
* 在某些标准控制字符之后插入延迟
* 展开制表符
* 为仅大写终端提供转换
* 把回显的非图形 ASCII 字符显示为形如 “^X” 的两字符序列（即 ASCII 脱字符后跟一个与该控制字符相关的可打印 ASCII 字符）

进程可以通过控制请求逐一停用这些格式化服务。


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