Linux numerical operations: let, (()), [ ] detailed explanation

In the Bash shell environment, you can use let, (( )) and [] to perform basic arithmetic operations. When performing advanced operations, the two tools expr and bc will also be very useful. You can use ordinary variable assignment methods to define a value, in which case it will be stored as a string. However, we can use some methods to make it operate like numbers

(1) The let command can directly perform basic arithmetic operations. When using let, there is no need to add $ before the variable name,

, for example,

[rhx@localhost Test]$ source 1.3.2.sh
[rhx@localhost Test]$ let result=no1+no2
[rhx@localhost Test]$ echo $result

self-increment, self-decrement, increment by step size

[rhx@localhost Test]$ let no1++
[rhx@localhost Test]$ let no1--
[rhx@localhost Test]$ let no1+=6
[rhx@localhost Test]$ let no1-=6

The usage of operator [] is similar to the let command:

[rhx@localhost Test]$ reslut=$[ no1+no2 ]

You can also use the $ prefix in [] , for example:

[rhx@localhost Test]$ reslut=$[ $no1+5

You can also use (()), but when using (()), the variable You need to add $ before the name:

result=$(( no1 + 50 ))
expr同样可以用于基本算术操作：
result=`expr 3 + 4`
result=$(expr $no1 + 5)

The above methods can only be used for integer operations and do not support floating point numbers.

(2) bc is an advanced tool for mathematical operations. This precision calculator contains a large number of options. You can use it to perform floating point operations and apply some advanced functions:

[rhx@localhost Test]$ echo "4*0.56" | bc

Other parameters can be placed before the specific operation to be performed, with semicolons as delimiters, Passed to bc via stdin.
Set decimal precision. In the example below, the parameter scale=2 sets the number of decimal places to 2. Therefore,

bc will output a value with two decimal places.

[rhx@localhost Test]$ echo "scale=2;3/8"|bc

# Base conversion. Use bc to convert one base system to another. Let's see how to convert decimal to binary, and then convert binary back to decimal:
#!/bin/bash

Purpose: Number conversion

[rhx@localhost Test]$ nu=100
[rhx@localhost Test]$ echo "obase=2;$nu"|bc

 Calculate squares and square roots.
echo "sqrt(100)" | bc #Square root
echo "10^10" | bc #Square

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