如何在 Bash 中比较两个浮点数? [英] How can I compare two floating point numbers in Bash?

问题描述

我正在努力比较 Bash 脚本中的两个浮点数.我有两个变量，例如

I am trying hard to compare two floating point numbers within a Bash script. I have two variables, e.g.

let num1=3.17648e-22
let num2=1.5

现在，我只想对这两个数字做一个简单的比较:

Now, I just want do a simple comparison of these two numbers:

st=`echo "$num1 < $num2" | bc`
if [ $st -eq 1]; then
  echo -e "$num1 < $num2"
else
  echo -e "$num1 >= $num2"
fi

不幸的是，我在正确处理 num1 时遇到了一些问题，它可能是电子格式".

Unfortunately, I have some problems with the right treatment of the num1 which can be of the "e-format".

推荐答案

更方便

使用 Bash 的数字上下文可以更方便地做到这一点:

More conveniently

This can be done more conveniently using Bash's numeric context:

if (( $(echo "$num1 > $num2" |bc -l) )); then
  …
fi

说明

通过基本的计算器命令bc 返回 1 或 0.

选项-l等价于--mathlib；它加载标准数学库.

The option -l is equivalent to --mathlib; it loads the standard math library.

将整个表达式括在双括号 (( )) 之间会将这些值分别转换为 true 或 false.

Enclosing the whole expression between double parenthesis (( )) will translate these values to respectively true or false.

请确保安装了bc基本计算器包.

Please, ensure that the bc basic calculator package is installed.

警告:指数符号应写成*10^；不是E，也不是e.

Caveat: Exponential notation should be written as *10^; not E, nor e.

例如:

$ echo "1*10^3==1000" |bc
1

然而

$ echo "1E3==1000" |bc
0

克服此bc 限制的策略在此处讨论.

Strategies to overcome this bc limitation are discussed here.

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