Arrays in the shell

Arrays are not used very often in the shell, but are very useful, let's take a look at some of the uses of arrays in the shell:

2. Define array a= (1 2 3 4 5); Print array echo ${a[@]}
   The contents of the array can be either numbers or letters, as shown in the following example:

   [[email protected] ~]# a=(1 2 3 4 5)[[email protected] ~]# echo $a     //可以看到使用这种方式返回不了数组的值1[[email protected] ~]# echo ${a[@]}1 2 3 4 5

4. echo ${#a [@]} Gets the number of elements in the array

   [[email protected] ~]# echo ${#a[@]}    //在打印数组命令中嵌入一个#号5[[email protected] ~]#

6. echo ${a[2]} reads the third element, array starting from 0

   [[email protected] ~]# echo ${a[2]}   //读取数组第三个元素，下标为23[[email protected] ~]# echo ${a[1]}   //读取数组第二个元素，下标为12[[email protected] ~]# echo ${a[0]}    //读取数组第一个元素，下标为0，下标都是从0开始的1[[email protected] ~]#

8. echo ${a[*]} equals ${a[@]} displays the entire array

   [[email protected] ~]# echo ${a[*]}   //使用*或@来表示数组的所有元素1 2 3 4 5[[email protected] ~]#

10. Array element Assignment command a[1]=100; Echo ${a[@]}

    [[email protected] ~]# a[1]=100 [[email protected] ~]# echo ${a[1]}100[[email protected] ~]# echo ${a[*]}1 100 3 4 5[[email protected] ~]#

12. a[5]=2; Echo ${a[@]} An element is added automatically if the subscript does not exist

    [[email protected] ~]# a=(1 2 3 4 5)[[email protected] ~]# echo ${a[*]}1 2 3 4 5[[email protected] ~]# a[5]=6[[email protected] ~]# echo ${a[*]}1 2 3 4 5 6[[email protected] ~]#

14. The deletion of the array uset A; Unset A[1]

    [[email protected] ~]# unset a[4]            //删除其中某一个元素，这里删除的是第5个元素[[email protected] ~]# echo ${a[*]}1 100 3 4[[email protected] ~]# unset a               //删除数组a中的所有元素[[email protected] ~]# echo ${a[*]}        [[email protected] ~]#

16. array Shard
    2. a= ( seq 1 5 )
    3. Echo ${a[@]:0:3} starts with the first element, intercepts 3

         [[Email p  Rotected] ~]# a= (' seq 1 ') [[email protected] ~]# echo ${a[*]}1 2 3 4 5 6 7 8 9 101 2 3  

    4. Echo ${a[@]:1:4} starts with the second element, intercepts 4

         2 3 4[[email protected] ~]#  

    5. Echo ${a[@]:0-3:2} Starting from the 3rd element, intercept 2

         [[email protected] ~]# echo ${a[@]}1 2 3 4 5 6 7 8 9 10[[email protected] ~]# echo ${a [@]:0-3:2}//Here with 0-3 for the 3rd element, 0 cannot omit 8 9[[email protected] ~]#  

18. Array substitution
    2. Echo ${A[@]/8/6}

       [[email protected] ~]# a=(`seq 1 10`) [[email protected] ~]# echo ${a[@]}1 2 3 4 5 6 7 8 9 10[[email protected] ~]# echo ${a[@]/8/6}    //将8替换为61 2 3 4 5 6 7 6 9 10[[email protected] ~]# echo ${a[@]}    //替换后a的值并未发生变化1 2 3 4 5 6 7 8 9 10

    3. A= (${A[@]/8/6})

       [[email protected] ~]# echo ${a[@]}1 2 3 4 5 6 7 8 9 10[[email protected] ~]# a=(${a[@]/8/6})    //将8替换为6后，将结果赋值给数组a[[email protected] ~]# echo ${a[@]}    //这时a的值发生了变化1 2 3 4 5 6 7 6 9 10[[email protected] ~]#

Arrays in the shell