击：一个字符串中提取部分 [英] Bash : extracting part of a string

问题描述

说我有字符串内存使用：19.54M
我将如何从中提取了19.54？
所以我需要将其存储在一个变量，并与下一次迭代的值进行比较的19.54会经常发生变化。

Say I have the string "Memory Used: 19.54M" How would I extract the 19.54 from it? The 19.54 will change frequently so i need to store it in a variable and compare it with the value on the next iteration.

我想我需要的grep和正则表达式的某种组合，但我从来没有真正理解正则表达式。

I imagine I need some combination of grep and regex, but I never really understood regex..

推荐答案

您可能想的提取物的它，而不是的删除的它。您可以使用参数扩展来提取值：

You probably want to extract it rather than remove it. You can use the Parameter Expansion to extract the value:

var="Memory Used: 19.54M"
var=${var#*: }            # Remove everything up to a colon and space
var=${var%M}              # Remove the M at the end

需要注意的是bash的只能比较整数，它没有浮点算术支持。

Note that bash can only compare integers, it has no floating point arithmetics support.

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