Merge pull request #29693 from lkxed/20230703-0-Bash-Basics-Series-4-Arithmetic-Operations

[手动选题][tech]: 20230703.0 ⭐️⭐️ Bash Basics Series 4 Arithmetic Operations.md

sources/tech/20230703.0 ⭐️⭐️ Bash Basics Series 4 Arithmetic Operations.md

@@ -0,0 +1,223 @@
+[#]: subject: "Bash Basics Series #4: Arithmetic Operations"
+[#]: via: "https://itsfoss.com/bash-arithmetic-operation/"
+[#]: author: "Abhishek Prakash https://itsfoss.com/author/abhishek/"
+[#]: collector: "lkxed"
+[#]: translator: " "
+[#]: reviewer: " "
+[#]: publisher: " "
+[#]: url: " "
+
+Bash Basics Series #4: Arithmetic Operations
+======
+
+You can do a lot of things with bash scripts. Performing simple arithmetic operations with the variables is one of them.
+
+The syntax for arithmetic operations in the bash shell is this:
+
+```
+$((arithmetic_operation))
+```
+
+Let's say you have to calculate the sum of two variables. You do it like this:
+
+```
+sum=$(($num1 + $num2))
+```
+
+There is no restriction on the use of white space inside the (()). You can use `$(( $num1+ $num2))`, `$(( $num1+ $num2 ))` or `$(( $num1+ $num2 ))`. It all will work the same.
+
+Before I discuss it in detail with examples, let me share the arithmetic operators it supports.
+
+### Basic arithmetic operators in Bash
+
+Here's a list of the arithmetic operators in the Bash shell.
+
+| Operator | Description |
+| :- | :- |
+| + | Addition |
+| - | Subtraction |
+| * | Multiplication |
+| / | Integer division (without decimal) |
+| % | Modulus division (only remainder) |
+| ** | Exponentiation (a to the power b) |
+
+> 🚧 Bash does not support floating points (decimals). You'll have to use other commands like`bc`to deal with them.
+
+### Addition and subtraction in bash
+
+Let's see it by writing a script that takes two numbers from the user and then prints their sum and subtraction.
+
+```
+#!/bin/bash
+
+read -p "Enter first number: " num1
+read -p "Enter second number: " num2
+
+sum=$(($num1+$num2))
+sub=$(($num1-$num2))
+echo "The summation of $num1 and $num2 is $sum"
+echo "The substraction of $num2 from $num1 is $sub"
+```
+
+I believe you are familiar with using the read command to [accept user input in bash][1] from the previous chapter.
+
+You should focus on these two lines:
+
+```
+sum=$(($num1+$num2))
+sub=$(($num1-$num2))
+```
+
+Save this script as `sum.sh` and run it. Give it some inputs and check the result.
+
+![Example of addition and subtraction in Bash shell script][2]
+
+### Multiplication in bash
+
+Let's move to multiplication now.
+
+Here's a sample script that converts kilometers into meters (and troubles US readers :D). For reference, 1 kilometer is equal to 1000 meters.
+
+```
+#!/bin/bash
+
+read -p "Enter distance in kilometers: " km
+meters=$(($km*1000))
+
+echo "$km KM equals to $meters meters"
+```
+
+Save the script as `multi.sh`, give it execute permission and run it. Here's a sample output:
+
+![Multiplication in bash script][3]
+
+Looks good, no? Let's move on to division.
+
+### Division in bash scripts
+
+Let's see division with a very simple script:
+
+```
+#!/bin/bash
+
+num1=50
+num2=5
+
+result=$(($num1/$num2))
+
+echo "The result is $result"
+```
+
+You can easily guess the result:
+
+```
+The result is 10
+```
+
+That's fine. But let's change the numbers and try to divide 50 by 6. Here's what it shows as result:
+
+```
+The result is 8
+```
+
+**But that's not correct.** The correct answer should be 8.33333.
+
+That's because bash only deals with integers by default. You need additional CLI tools to handle floating points (decimals).
+
+The most popular tool is [bc][4] which is quite a powerful calculator language to deal with mathematical operations. However, you don't need to go into detail for now.
+
+You have to 'echo' the arithmetic operation to bc via pipe:
+
+```
+echo "$num1/$num2" | bc -l
+```
+
+So, the previous script is modified into:
+
+```
+#!/bin/bash
+
+num1=50
+num2=6
+
+result=$(echo "$num1/$num2" | bc -l)
+
+echo "The result is $result"
+```
+
+And now you get the result:
+
+```
+The result is 8.33333333333333333333
+```
+
+Notice the `result=$(echo "$num1/$num2" | bc -l)`, it now uses the command substitution that you saw in [chapter 2 of this series][5].
+
+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:
+
+```
+result=$(echo "scale=3; $num1/$num2" | bc -l)
+```
+
+Let's see some more examples of floating points in bash.
+
+### Handling floating points in bash scripts
+
+Let's modify the `sum.sh` script to handle floating points.
+
+```
+#!/bin/bash
+
+read -p "Enter first number: " num1
+read -p "Enter second number: " num2
+
+sum=$( echo "$num1+$num2" | bc -l)
+sub=$( echo "scale=2; $num1-$num2" | bc -l)
+echo "The summation of $num1 and $num2 is $sum"
+echo "The substraction of $num2 from $num1 is $sub"
+```
+
+Try running it now and see if handles floating points properly or not:
+
+![Floating points in bash script][6]
+
+### 🏋️🤸 Exercise time
+
+Time to do some maths and bash exercises together.
+
+**Exercise 1**: Create a script that accepts input in GB and outputs its equivalent value in MB and KB.
+
+**Exercise 2**: Write a script that takes two arguments and outputs the result in exponential format.
+
+So, if you enter 2 and 3, the output will be 8, which is 2 to the power 3.
+
+**Hint**: Use the exponentiation operator **
+
+**Exercise 3**: Write a script that converts Centigrade to Fahrenheit.
+
+**Hint**: Use the formula F = C x (9/5) + 32. You'll have to use `bc` command here.
+
+You can discuss the exercises and their solution in the community.
+
+In the next chapter, you'll [learn about arrays in Bash][7]. Stay tuned.
+
+--------------------------------------------------------------------------------
+
+via: https://itsfoss.com/bash-arithmetic-operation/
+
+作者：[Abhishek Prakash][a]
+选题：[lkxed][b]
+译者：[译者ID](https://github.com/译者ID)
+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
+[3]: https://itsfoss.com/content/images/2023/07/multiplication-bash-script.png
+[4]: https://www.gnu.org/software/bc/manual/html_mono/bc.html
+[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/