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📜  Bash算术运算符

📅  最后修改于: 2020-12-29 06:03:50             🧑  作者: Mango

Bash算术运算符

在本主题中，我们将了解如何在Bash中使用算术运算运算符。

根据我们希望通过脚本获得的结果类型，我们有时可能需要应用算术运算运算符。像变量一样，它们也很容易应用。在bash脚本中，我们可以对数值执行算术运算以获得所需的结果。

Bash Shell支持11种算术运算运算符。

查看下表，其中展示了每种算术运算运算符的语法，描述和示例：

Operator Description Examples
+ Addition, measures addition of numbers (operands) 
$(( 10 + 3 )), result=13
– Substraction, measures subtraction of second operand from first 
$(( 10 - 3 )), result=7
* Multiplication, measures the multiplication of operands. 
$(( 10 * 3 )), result=30
/ Division, measures the division of first operand by second operand and and return quotient. 
$(( 10 / 3 )), result=3
** Exponentiation, measures the result of second operand raised to the power of first operand. 
$((  10 ** 3 )), result=1000
% Modulo, measures remainder when the first operand is divided by second operand. 
$(( 10 % 3 )), result=1
+= Increment Variable by Constant- used to increment the value of first operand by the constant provided. 
x=10
let "x += 3"
echo $x
result=13
-= Decrement Variable by Constant- used to decrement the value of first operand by the constant provided. 
x=10
let "x -= 3"
echo $x
result=7
*= Multiply Variable by Constant- used to multiply the value of the first operand by the constant provided. 
x=10
let "x *= 3"
echo $x
result=30
/= Divide Variable by Constant- used to calculate the value of (variable / constant) and store the result back to variable. 
x=10
let "10 /= 3"
echo $x
result=3
%= Remainder of Dividing Variable by Constant- used to calculate the value of (variable % constant) and store the result back to variable. 
x=10
let "10 %= 3"
echo $x
result=1

在Bash中执行算术运算

有很多选项可以在bash shell上执行算术运算。下面提供了一些我们可以用来执行算术运算的选项：

双括号

双括号是在Bash shell中执行基本算术运算的最简单机制。我们可以使用带或不带前导$的双括号来使用此方法。

句法

((expression))

我们可以采用四种不同的方法来实现所需的目标。查看下面给出的方法，以了解如何使用双括号机制(假设我们想将数字10和3相加)：

方法1

Sum=$((10+3))
echo "Sum = $Sum"

方法2

((Sum=10+3))
echo "Sum = $Sum"

方法3

Num1=10
Num2=3
((Sum=Num1+Num2))
echo "Sum = $Sum"

方法4

Num1=10
Num2=3
Sum=$((Num1+Num2))
echo "Sum = $Sum"

所有这些方法将提供与以下相同的输出：

Sum = 13

下面是一个示例，演示在Bash shell脚本中对运算符使用双括号的情况：

Bash脚本

#!/bin/bash

x=8
y=2
echo "x=8, y=2"
echo "Addition of x & y"
echo $(( $x + $y ))
echo "Subtraction of x & y"
echo $(( $x - $y ))
echo "Multiplication of x & y"
echo $(( $x * $y ))
echo "Division of x by y"
echo $(( $x / $y ))
echo "Exponentiation of x,y"
echo $(( $x ** $y ))
echo "Modular Division of x,y"
echo $(( $x % $y ))
echo "Incrementing x by 5, then x= "
(( x += 5 )) 
echo $x
echo "Decrementing x by 5, then x= "
(( x -= 5 ))
echo $x
echo "Multiply of x by 5, then x="
(( x *= 5 ))
echo $x
echo "Dividing x by 5, x= "
(( x /= 5 ))
echo $x
echo "Remainder of Dividing x by 5, x="
(( x %= 5 ))
echo $x

输出量

让建设

Let是Bash的内置命令，它允许我们执行算术运算。它遵循基本格式：

句法

let

下面给出一个示例，说明如何在Bash脚本中使用let命令：

Bash脚本

#!/bin/bash

x=10
y=6
z=0
echo "Addition"
let "z = $(( x + y ))"
echo "z= $z"

echo "Substraction"
let "z = $((x - y ))"
echo "z= $z"

echo "Multiplication"
let "z = $(( x * y ))"
echo "z = $z"

echo "Division"
let "z = $(( x / y ))"
echo "z = $z"

echo "Exponentiation"
let "z = $(( x ** y ))"
echo "z = $z"

echo "Modular Division"
let "z = $(( x % y ))"
echo "z = $z"

let "x += 5"
echo "Incrementing x by 5, then x= "
echo $x

let "x -= 5"
echo "Decrementing x by 5, then x= "
echo $x

let "x *=5"
echo "Multiply of x by 5, then x="
echo $x

let "x /= 5"
echo "Dividing x by 5, x= "
echo $x

let "x %= 5"
echo "Remainder of Dividing x by 5, x="
echo $x

输出量

反引号

在bash脚本中，还可以使用反引号和expr(称为通用表达式求值器)执行算术扩展。 “ expr”类似于“ let”，但是不会将结果保存到变量中。它直接打印结果。与let不同，我们不需要将表达式用引号引起来。我们需要在表达式的项目之间使用空格。重要的是要注意，我们应该在命令替换中使用'expr'将输出保存到变量中。

我们也可以不使用“反引号”而使用“ expr”。

句法

`expr item1 operator item2`
or
expr item1 operator item2

下面给出一个示例，说明如何在Bash脚本中使用反引号和expr：

Bash脚本程序

#!/bin/bash
#Basic arithmetic using expr

echo "a=10, b=3"
echo "c is the value of addition c=a+b"
a=10
b=3
echo "c= `expr $a + $b`"

输出量

结论

在本主题中，我们讨论了如何使用算术运算运算符执行算术运算。