The ruleref for command2 is commented out because it is a placeholder for an as yet nonexistent master rule.

command2的ruleref被注释掉了，因为它只是一个还不存在的主规则的占位符。

youdao

In order to use the output of a command, command1, as input to a filter, command2, you connect the commands using the pipe operator (|).

要将命令command1的输出作为过滤器command2的输入，您需要使用管道操作符(|)连接两个命令。

youdao

In the hypothetical pipeline in Listing 10, command2 and command3 both have parameters, while command3 USES the - parameter alone to signify input from stdin.

在清单10的假设管道线中，command2和command3都带有参数，但command3仅使用-参数表示来自stdin的输入。

youdao