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Shell进阶技巧

 1 year ago
source link: https://bajie.dev/posts/20220609-shell_tips/
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Shell进阶技巧

2022-06-09 2 分钟阅读

Shell脚本的进阶技巧：

一、String 类的技巧

String类当作数组来使用，注意范围的下标，0:4，4最后要被踢掉，实际是0-3，共4个字符：

string="Bash is great!"

echo ${string:8} # great!
echo ${string:0:4} # Bash
echo ${string:8:-1} # great (-1: upto 1st element from right)
fallback

数组的长度：

string="Bash is great!";
len=${#string}
echo "len = $len"
fallback

字符串的替换：

string="Bash is great!!"
echo ${string/Bash/GNU Bash} # GNU Bash is great!!
echo ${string//!/.} # Bash is great..
fallback

大小写替换:

string="Bash"
echo ${string^^} # BASH
echo ${string,,} # bash
fallback

按index存取数组中字符在shell中不可用，但是可以用function变相实现：

function charAt() {
    string=$1
    i=$2
    echo ${string:i:1}
}
echo $(charAt "Hello" 2) # l
echo $(charAt "Hello" 1) # e
fallback

二、数组和字典

定义一个数组并且遍历它：

A=(2 4 5 6 4)
for i in ${A[@]}; do
    echo -n "${i} " # 2 4 5 6 4
done
fallback

同样对数组进行切割：

A=(2 4 5 6 4)
echo ${A[@]:2:3} # 5 6 4
echo ${A[@]:0:1} # 2
fallback

Bash 中的数组需要使用 [@] 符号来引用整个数组，可以用简洁的语法对数组增加元素

A=(1 2 3)
A+=(4)
echo ${A[@]} # 1 2 3 4
A+=(5 6)
echo ${A[@]} # 1 2 3 4 5 6
fallback

字典也一样

declare -A D
D=(["one"]=1 ["two"]=2 ["three"]=3)
for i in ${!D[@]}; do
    echo "$i -> ${D[$i]}" # one -> 1 ....
done
fallback

三、数学计算

简单的数学计算可以用 $((...)) 来完成：

a=10
b=5

echo "$a + $b = $((a + b))" # 10 + 5 = 15
echo "$a - $b = $((a - b))" # 10 - 5 = 5
echo "$a x $b = $((a * b))" # 10 x 5 = 50
echo "$a / $b = $((a / b))" # 10 / 5 = 2
echo "$a % $b = $((a % b))" # 10 % 5 = 0
fallback

或者借助复杂一点的 bc 来完成：

a=10
b=5.7

echo "$a / $b = $(echo "scale = 2; $a / $b" | bc)" # 10 / 5.7 = 1.75
fallback

随机数的产生：

echo $(($RANDOM % 10)) # Random number between 0 and 10
fallback

控制输入变量：

read -p "Enter your name: " name
echo "Hello, $name"
fallback

如果要输入数组：

read -p "Enter numbers: " -a A
echo ${A[@]}
fallback

借助上面的技巧，我们可以写出一些复杂的 shell 脚本了


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