linux的shell基础之数值运算的3种方法

朱雀 2024-04-18 19:02 50阅读 0赞

# 一、linux中shell的数值运算的3种方法： #

## 1. declare -i （了解，不推荐使用） ##

shell中所有的变量默认是字符串型，所以可以利用declare来将变量声明为整数型，就可以运算了  
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[root@localhost ~]# a=9
    [root@localhost ~]# b=7
    [root@localhost ~]# declare -i c=$a+$b
    [root@localhost ~]# echo $c
    16
    [root@localhost ~]#

## 2.使用expr和let数值运算工具（细节多，易出错，不推荐） ##

### 2.1 expr工具 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 1]  
**注意：+两端必须空格**

[root@localhost ~]# a=9
    [root@localhost ~]# b=7
    [root@localhost ~]# d=$(expr $a + $b ) 
    [root@localhost ~]# echo $d
    16

细节多，易出错，不推荐

### 2.2 let工具： ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 2]

[root@localhost ~]# a=11
    [root@localhost ~]# b=22
    [root@localhost ~]# let c=$a+$b
    [root@localhost ~]# echo $c
    33
    [root@localhost ~]#

推荐指数：3颗星

## 3.使用双小括号 $(( 运算式))或 $\[运算式\] ##

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[root@localhost ~]# a=34
    [root@localhost ~]# b=56
    [root@localhost ~]# c=$(($a+$b))
    [root@localhost ~]# echo $c
    90

**推荐使用$(( 运算式))**

# 二、shell中的运算符 #

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