Linux shell number variables add All In One

bash / zsh

error ❌

# string number / 字符串数字
$ var1=1
$ var2=2

$ echo $var1
# 1
$ echo $var2
# 2

$ echo $var1$var2
# 12
$ echo $var1 + $var2
# 1 + 2

$ echo ${var1 + var2}
# zsh: bad substitution ❌
$ echo ${var1} + ${var2}
# 1 + 2

solutions ✅

1. declare -i

$ var1=1
$ echo $var1
# 1
$ var1+=1
$ echo $var1
# 11

# 声明为 integer 整数类型 ✅ `declare -i`
$ declare -i num1
$ num1=1
$ echo $num1
# 1
$ num1+=1
$ echo $num1
# 2

2. Use $(()) for bash arithmetic expansion.

使用 $(()) 进行 bash 算术扩展。

$ var1=1 
$ var2=2

$ echo $var1 + $var2
# 1 + 2
$ echo $(($var1 + $var2))
# 3

https://infoheap.com/bash-add-number-variable/

3. ??? 逆波兰表达式

4. let

# let

https://stackoverflow.com/questions/6348902/how-can-i-add-numbers-in-a-bash-script

https://linux.die.net/man/1/dc

https://www.computerhope.com/unix/bash/let.htm

(

标签：var1,template,var2,echo,https,com,bash
From： https://www.cnblogs.com/xgqfrms/p/17009813.html