inet addr的正则表达式失败 [英] Regex for inet addr failed

问题描述

在Ubuntu 16.04中，我运行了 ifconfig ，并在 inet addr中查看了我的外部IP：MY_IP 。

In Ubuntu 16.04 I ran ifconfig and saw my external ip as in inet addr:MY_IP.

我试图通过以下方式将其挖到变量中：

I tried to "dug" it right into a variable in these ways:

ipa=$(ifconfig | grep "inet addr:\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b")

和：

ipa=$(ifconfig | grep "inet addr:\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.")

这些方法有效：

ipa=$(ifconfig | grep -Po 'inet addr:\K[^\s]+' | grep -v '^127')

和

ipa=$(ifconfig | grep -A 1 eth0 | grep -Po "inet addr:(\d{1,3}\.){3}\d{1,3}" | cut -f2 -d:)

但我想请知道，在我的前两次尝试中我错过了什么。

But I would like to know, please, what I've missed in my first 2 tryings.

是否有一种方法来使用一个 grep 有4个组（类似于前2个的概念），确实可以在POSIX BRE中使用吗？

Is there a way to use one grep with 4 groups (similar to the concept of the first 2) that will indeed work in POSIX BRE?

推荐答案

您可以使用旧式 \< 替换 \b 虽然它似乎不是POSIX。

You can replace \b with the old-style \< though it doesn't seem to be POSIX.

另请注意，交替（a | b）是 grep -E 功能。在POSIX grep中，你可以反斜杠这些结构（很奇怪），但我只需要使用 grep -E 。

Notice also that alternation (a|b) is a grep -E feature. In POSIX grep, you can backslash those constructs (weirdly) but I'd just go with grep -E.

ipa=$(ifconfig | grep -E "inet addr:\<(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.")

没有但是，在那里需要一个单词边界;你已经知道左边的字符是冒号，右边的字符是数字。

There is no need for a word boundary there, though; you already know the character to the left is a colon and the one to the right is a digit.

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