Shell数组

不念不忘少年蓝@ 2022-08-18 03:10 222阅读 0赞

# 1.Shell数组的定义 #

## 1.1空数组定义 ##

#define a null array
    null_arr=()
    null_arr[0]=test
    null_arr[1]=2
    echo ${null_arr[1]}  $null_arr
    
    #2 test

**注意：**

1.  如果直接打印数组名$null\_arr，那么只会输出数组的第一个元素，
2.  数组元素的数据类型可以不同。

## 1.2非空数组定义 ##

#define a array with 5 elements
    arr=(1 2 3 4 5)

**注意：数组元素是以“ ”（空格符）隔开，而不是“,”（逗号）。**

# 2.数组的长度 #

#calculate the length of the array
    len=${#arr[@]}
    echo "Length of array: $len"
    
    #Length of array: 5

# 3.数组的遍历 #

## 3.1用像C语言中的for遍历 ##

不过，用这种方式需要计算数组的长度。

#traverse the array with C-for
    for ((i = 0; i < len; i++));do
    {
        echo $i"th element: ${arr[i]}"
    }
    done
    
    #0th element: 1
    #1th element: 2
    #2th element: 3
    #3th element: 4
    #4th element: 5

## 3.2用下标索引遍历 ##

#traverse the array with its index
    for i in "${!arr[@]}";do
    {
        echo $i"th element: ${arr[i]}"
    }
    done
    
    #0th element: 1
    #1th element: 2
    #2th element: 3
    #3th element: 4
    #4th element: 5

## 3.3直接访问元素 ##

#traverse the array with for
    for val in ${arr[@]};do
    {
        echo $val       
    }
    done
    
    #1
    #2
    #3
    #4
    #5

## 3.4while-do遍历 ##

#traverse the array with while
    i=0
    while [ $i -lt ${#arr[@]} ];do
    {
        echo $i"th element: ${arr[i]}"
        #i=$(($i + 1))
        #let ++i
        let i++
    }
    done
    
    #0th element: 1
    #1th element: 2
    #2th element: 3
    #3th element: 4
    #4th element: 5

如果只是打印数组的话，可以用下面的快捷方式，注意$\{arr\[\*\]\}和$\{arr\[@\]\}是等价的。

echo "My array: ${arr[*]}"
    
    echo "My array: ${arr[@]}"

# 4.shell数组的特色 #

shell数组的特色

1.  shell数组可以给任何位置赋值，而未被赋值的位置是空（没有任何元素，包括空格等）。
2.  shell数组的长度不受定义时的长度限制。
3.  shell数组的长度指的是数组中元素的个数。并且对第一条仍然适用，即空位置不算长度。
4.  shell数组中元素类型可以不同。

arr[10]=test
    echo "current length of the array: ${#arr[@]}"
    echo "8th and 9th elements of the array are: ${arr[8]}, ${arr[9]}"
    echo "10th element of the array: ${arr[10]}"
    
    #current length of the array: 6
    #8th and 9th elements of the array are: , 
    #10th element of the array: test

完整代码：

#!/usr/bin/env bash
    #define a null array
    null_arr=()
    null_arr[0]=test
    null_arr[1]=2
    echo ${null_arr[1]} $null_arr
    #define a array with 5 elements
    arr=(1 2 3 4 5)
    #calculate the length of the array
    len=${#arr[@]}
    echo "Length of array: $len"
    #traverse the array with C-for
    for ((i = 0; i < len; i++));do
    {
    echo $i"th element: ${arr[i]}"
    }
    done
    #traverse the array with its index
    for i in "${!arr[@]}";do
    {
    echo $i"th element: ${arr[i]}"
    }
    done
    #traverse the array with for
    for val in ${arr[@]};do
    {
    echo $val
    }
    done
    #traverse the array with while
    i=0
    while [ $i -lt ${#arr[@]} ];do
    {
    echo $i"th element: ${arr[i]}"
    #i=$(($i + 1))
    #let ++i
    let i++
    }
    done
    arr[10]=test
    echo "current length of the array: ${#arr[@]}"
    echo "8th and 9th elements of the array are: ${arr[8]}, ${arr[9]}"
    echo "10th element of the array: ${arr[10]}"