If the output stream was stdout, and if it was piped to another process (at the command line level), the selected pages will become the input to that process.
如果输出流是标准输出，并且由管道输送至另一个进程(在命令行级别)，则选定的页将成为该进程的输入。
2
While in command mode, you can use the >> command to add a level of indentation to an existing line or the << command to remove a level.
在命令模式下，可以使用 >> 命令让现有的一行增加一级缩进，使用 << 命令减少一级缩进。
3
Unit and command line testing of low-level components.