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[#]: subject: "Bash Basics Series #4: Arithmetic Operations"
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[#]: via: "https://itsfoss.com/bash-arithmetic-operation/"
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[#]: author: "Abhishek Prakash https://itsfoss.com/author/abhishek/"
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[#]: collector: "lkxed"
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[#]: translator: "geekpi"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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Bash Basics Series #4: Arithmetic Operations
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======
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You can do a lot of things with bash scripts. Performing simple arithmetic operations with the variables is one of them.
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The syntax for arithmetic operations in the bash shell is this:
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```
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$((arithmetic_operation))
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```
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Let's say you have to calculate the sum of two variables. You do it like this:
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```
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sum=$(($num1 + $num2))
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```
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There is no restriction on the use of white space inside the (()). You can use `$(( $num1+ $num2))`, `$(( $num1+ $num2 ))` or `$(( $num1+ $num2 ))`. It all will work the same.
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Before I discuss it in detail with examples, let me share the arithmetic operators it supports.
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### Basic arithmetic operators in Bash
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Here's a list of the arithmetic operators in the Bash shell.
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| Operator | Description |
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| :- | :- |
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| + | Addition |
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| - | Subtraction |
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| * | Multiplication |
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| / | Integer division (without decimal) |
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| % | Modulus division (only remainder) |
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| ** | Exponentiation (a to the power b) |
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> 🚧 Bash does not support floating points (decimals). You'll have to use other commands like`bc`to deal with them.
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### Addition and subtraction in bash
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Let's see it by writing a script that takes two numbers from the user and then prints their sum and subtraction.
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```
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#!/bin/bash
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read -p "Enter first number: " num1
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read -p "Enter second number: " num2
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sum=$(($num1+$num2))
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sub=$(($num1-$num2))
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echo "The summation of $num1 and $num2 is $sum"
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echo "The substraction of $num2 from $num1 is $sub"
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```
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I believe you are familiar with using the read command to [accept user input in bash][1] from the previous chapter.
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You should focus on these two lines:
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```
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sum=$(($num1+$num2))
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sub=$(($num1-$num2))
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```
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Save this script as `sum.sh` and run it. Give it some inputs and check the result.
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![Example of addition and subtraction in Bash shell script][2]
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### Multiplication in bash
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Let's move to multiplication now.
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Here's a sample script that converts kilometers into meters (and troubles US readers :D). For reference, 1 kilometer is equal to 1000 meters.
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```
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#!/bin/bash
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read -p "Enter distance in kilometers: " km
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meters=$(($km*1000))
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echo "$km KM equals to $meters meters"
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```
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Save the script as `multi.sh`, give it execute permission and run it. Here's a sample output:
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![Multiplication in bash script][3]
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Looks good, no? Let's move on to division.
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### Division in bash scripts
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Let's see division with a very simple script:
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```
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#!/bin/bash
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num1=50
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num2=5
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result=$(($num1/$num2))
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echo "The result is $result"
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```
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You can easily guess the result:
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```
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The result is 10
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```
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That's fine. But let's change the numbers and try to divide 50 by 6. Here's what it shows as result:
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```
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The result is 8
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```
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**But that's not correct.** The correct answer should be 8.33333.
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That's because bash only deals with integers by default. You need additional CLI tools to handle floating points (decimals).
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The most popular tool is [bc][4] which is quite a powerful calculator language to deal with mathematical operations. However, you don't need to go into detail for now.
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You have to 'echo' the arithmetic operation to bc via pipe:
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```
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echo "$num1/$num2" | bc -l
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```
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So, the previous script is modified into:
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```
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#!/bin/bash
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num1=50
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num2=6
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result=$(echo "$num1/$num2" | bc -l)
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echo "The result is $result"
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```
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And now you get the result:
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```
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The result is 8.33333333333333333333
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```
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Notice the `result=$(echo "$num1/$num2" | bc -l)`, it now uses the command substitution that you saw in [chapter 2 of this series][5].
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The `-l` option loads standard math library. By default, bc will go up to 20 decimal points. You can change the scale to something smaller in this way:
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```
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result=$(echo "scale=3; $num1/$num2" | bc -l)
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```
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Let's see some more examples of floating points in bash.
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### Handling floating points in bash scripts
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Let's modify the `sum.sh` script to handle floating points.
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```
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#!/bin/bash
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read -p "Enter first number: " num1
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read -p "Enter second number: " num2
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sum=$( echo "$num1+$num2" | bc -l)
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sub=$( echo "scale=2; $num1-$num2" | bc -l)
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echo "The summation of $num1 and $num2 is $sum"
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echo "The substraction of $num2 from $num1 is $sub"
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```
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Try running it now and see if handles floating points properly or not:
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![Floating points in bash script][6]
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### 🏋️🤸 Exercise time
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Time to do some maths and bash exercises together.
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**Exercise 1**: Create a script that accepts input in GB and outputs its equivalent value in MB and KB.
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**Exercise 2**: Write a script that takes two arguments and outputs the result in exponential format.
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So, if you enter 2 and 3, the output will be 8, which is 2 to the power 3.
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**Hint**: Use the exponentiation operator **
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**Exercise 3**: Write a script that converts Centigrade to Fahrenheit.
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**Hint**: Use the formula F = C x (9/5) + 32. You'll have to use `bc` command here.
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You can discuss the exercises and their solution in the community.
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In the next chapter, you'll [learn about arrays in Bash][7]. Stay tuned.
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--------------------------------------------------------------------------------
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via: https://itsfoss.com/bash-arithmetic-operation/
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作者：[Abhishek Prakash][a]
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选题：[lkxed][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://itsfoss.com/author/abhishek/
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[b]: https://github.com/lkxed/
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[1]: https://itsfoss.com/bash-pass-arguments/
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[2]: https://itsfoss.com/content/images/2023/07/addition-substraction-bash-script.png
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[3]: https://itsfoss.com/content/images/2023/07/multiplication-bash-script.png
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[4]: https://www.gnu.org/software/bc/manual/html_mono/bc.html
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[5]: https://itsfoss.com/bash-use-variables/
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[6]: https://itsfoss.com/content/images/2023/07/floating-point-bash.png
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[7]: https://itsfoss.com/bash-arrays/
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@ -0,0 +1,223 @@
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[#]: subject: "Bash Basics Series #4: Arithmetic Operations"
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[#]: via: "https://itsfoss.com/bash-arithmetic-operation/"
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[#]: author: "Abhishek Prakash https://itsfoss.com/author/abhishek/"
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[#]: collector: "lkxed"
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[#]: translator: "geekpi"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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Bash 基础知识系列 #4：算术运算
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======
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你可以使用 bash 脚本做很多事情。对变量执行简单的算术运算就是其中之一。
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bash shell 中算术运算的语法如下：
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```
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$((arithmetic_operation))
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```
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假设你必须计算两个变量的总和。你这样做：
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```
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sum=$(($num1 + $num2))
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```
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(()) 内空格的使用没有限制。你可以使用 `$(( $num1+ $num2))`、`$(( $num1+ $num2 ))` 或者 `$(( $num1+ $num2 ))`。它们都一样。
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在通过示例详细讨论之前，我先分享一下它支持的算术运算符。
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### Bash 中的基本算术运算符
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以下是 Bash shell 中算术运算符的列表。
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| 运算符 | 描述 |
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| :- | :- |
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| + | 加法 |
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| - | 减法|
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| * | 乘法|
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| / | 整数除法（不带小数） |
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| % | 模除法（仅余数）|
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| ** | 求幂（a 的 b 次方）|
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> 🚧 Bash 不支持浮点数（小数）。你必须使用其他命令（例如“bc”）来处理它们。
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### bash 中的加法和减法
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让我们通过编写一个脚本来看看它，该脚本从用户那里获取两个数字，然后打印它们的总和和减法。
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```
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#!/bin/bash
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read -p "Enter first number: " num1
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read -p "Enter second number: " num2
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sum=$(($num1+$num2))
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sub=$(($num1-$num2))
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echo "The summation of $num1 and $num2 is $sum"
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echo "The substraction of $num2 from $num1 is $sub"
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```
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我相信你熟悉上一章中使用 read 命令来[在 bash 中接受用户输入][1]。
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你应该关注这两行：
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```
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sum=$(($num1+$num2))
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sub=$(($num1-$num2))
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```
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将此脚本保存为 `sum.sh` 并运行它。给它一些输入并检查结果。
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![Example of addition and subtraction in Bash shell script][2]
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### bash 中的乘法
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现在让我们转向乘法。
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这是一个将公里转换为米的示例脚本（这给美国读者带来了麻烦：D）。作为参考，1 公里等于 1000 米。
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```
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#!/bin/bash
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read -p "Enter distance in kilometers: " km
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meters=$(($km*1000))
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echo "$km KM equals to $meters meters"
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```
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将脚本保存为 `multi.sh`，赋予其执行权限并运行它。这是一个示例输出：
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![Multiplication in bash script][3]
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看起来不错，不是吗？ 让我们继续进行除法。
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### bash 脚本中的除法
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让我们用一个非常简单的脚本来看看除法：
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```
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#!/bin/bash
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num1=50
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num2=5
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result=$(($num1/$num2))
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echo "The result is $result"
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```
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你很容易猜到结果：
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```
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The result is 10
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```
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没关系。但是让我们更改数字并尝试将 50 除以 6。结果如下：
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```
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The result is 8
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```
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**但这不正确。** 正确答案应该是 8.33333。
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这是因为 bash 默认情况下只处理整数。你需要额外的命令行工具来处理浮点（小数）。
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最流行的工具是[bc][4]，它是一种处理数学运算的非常强大的计算器语言。不过，你现在不需要关注细节。
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你必须通过管道将算术运算“回显”给 bc：
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```
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echo "$num1/$num2" | bc -l
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```
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于是，将之前的脚本修改为：
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```
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#!/bin/bash
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num1=50
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num2=6
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result=$(echo "$num1/$num2" | bc -l)
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echo "The result is $result"
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```
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现在你得到结果：
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```
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The result is 8.33333333333333333333
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```
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请注意 `result=$(echo "$num1/$num2" | bc -l)`，它现在使用你在[本系列第 2 章][5]中看到的命令替换。
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`-l` 选项加载标准数学库。默认情况下，bc 最多保留 20 位小数。你可以通过以下方式将比例更改为较小的值：
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```
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result=$(echo "scale=3; $num1/$num2" | bc -l)
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```
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让我们看看 bash 中浮点的更多示例。
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### 在 bash 脚本中处理浮点
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让我们修改 `sum.sh` 脚本来处理浮点。
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```
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#!/bin/bash
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read -p "Enter first number: " num1
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read -p "Enter second number: " num2
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sum=$( echo "$num1+$num2" | bc -l)
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sub=$( echo "scale=2; $num1-$num2" | bc -l)
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echo "The summation of $num1 and $num2 is $sum"
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echo "The substraction of $num2 from $num1 is $sub"
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```
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现在尝试运行它，看看是否可以正确处理浮点：
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![Floating points in bash script][6]
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### 🏋️🤸 练习时间
|
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是时候一起做一些数学和 bash 练习了。
|
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**练习 1**：创建一个脚本，接受以 GB 为单位的输入并以 MB 和 KB 为单位输出其等效值。
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**练习 2**：编写一个带有两个参数并以指数格式输出结果的脚本。
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因此，如果输入 2 和 3，输出将为 8，即 2 的 3 次方。
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**提示**：使用幂运算符**
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**练习 3**：编写一个将摄氏度转换为华氏度的脚本。
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||||
**提示**：使用公式 F = C x (9/5) + 32。你必须在此处使用 `bc` 命令。
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||||
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||||
你可以在社区中讨论练习及其方案。
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||||
在下一章中，你将[了解 Bash 中的数组][7]。敬请关注。
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--------------------------------------------------------------------------------
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||||
|
||||
via: https://itsfoss.com/bash-arithmetic-operation/
|
||||
|
||||
作者：[Abhishek Prakash][a]
|
||||
选题：[lkxed][b]
|
||||
译者：[geekpi](https://github.com/geekpi)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://itsfoss.com/author/abhishek/
|
||||
[b]: https://github.com/lkxed/
|
||||
[1]: https://itsfoss.com/bash-pass-arguments/
|
||||
[2]: https://itsfoss.com/content/images/2023/07/addition-substraction-bash-script.png
|
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[3]: https://itsfoss.com/content/images/2023/07/multiplication-bash-script.png
|
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[4]: https://www.gnu.org/software/bc/manual/html_mono/bc.html
|
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[5]: https://itsfoss.com/bash-use-variables/
|
||||
[6]: https://itsfoss.com/content/images/2023/07/floating-point-bash.png
|
||||
[7]: https://itsfoss.com/bash-arrays/
|
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