刷新sed内部的命令 [英] refresh the command inside sed

问题描述

sed 中的date命令不会在每一行上更新.

The date command inside sed isn't updating on each line.

我正在尝试学习 sed 和其他用于脚本编写的基本命令.在此示例中，我尝试在ping时间之后添加时间戳(这是另一个用户在上一个问题中提供的解决方案)，但是 date 命令似乎并没有在每一行上更新.我尝试阅读有关 sed 选项的信息，但到目前为止，我的所有尝试都没有成功

I'm trying to learn sed and other basic commands for scripting. In this example I'm trying to append a timestamp next to the ping time (a solution provided by another user in a previous question), but the date command doesn't seem to update on each line. I've tried to read about sed options, but all my attempts so far have been fruitless

ping 8.8.8.8 |sed --unbuffered"s/.* time = \([0-9 \.] * \).*/\ 1 $(date +％T)/"

我期待

85.2 10:59:26
140 10:59:27
231 10:59:28
97.7 10:59:29
117 10:59:30
80.9 10:59:31

但是我得到

85.2 10:59:26
140 10:59:26
231 10:59:26
97.7 10:59:26
117 10:59:26
80.9 10:59:26

推荐答案

问题是在外壳程序运行 sed 之前，仅对 $(date)进行一次评估..如果您希望它每次运行，请尝试使用 e 选项代替 sed .这是 sed 的GNU扩展.

The problem is that the $(date) is only evaluated once, before the shell runs sed. If you want it run each time, try the e option to the sed substitution. This is a GNU extension to sed.

$ ping 8.8.8.8 | sed --unbuffered  's/.*time=\([0-9\.]*\).*/echo \1 $(date +%T)/e'

或者如果您想避免 echo 和 $():

$ ping 8.8.8.8 | sed --unbuffered  's/.*time=\([0-9\.]*\).*/date "+\1 %T"/e'

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