5、 Array base

Shell An array of is an array of finite elements （ Variable or character content ） Give a name to , A collection of elements that are then numbered to distinguish them . This name is called the array name , The number used to distinguish different contents is called array subscript . The elements that make up the array （ Variable ） Elements called arrays , Sometimes called subscript variable An array is also a variable variable , Therefore, the array of related functions of variable substring is also applicable , By default, array subscripts are from 0 Start counting .

Array related knowledge through man bash Then search for Arrays To get to know .

1. Define an array

1) Statically named arrays

• Method 1[ recommend ] array1=(1 2 3)
• Method 2

array2=(
www.baidu.com
www.sina.com
)

• Method 3 array=([0]=one [1]=two [2]=three [3]=four)

2) Dynamic commands create arrays

array=($(ls))
array=(`ls`)

2. Print array

1) Print all elements ：

$(array[@])
$(array[*])

2) Print array length ：

$(#array[@])
$(#array[*])

3) Print a single element ：

$(array[i])

3. Add or modify array data

1) Add to change

array[0]=one
array[1]=two
array[2]=three

If the corresponding subscript value does not exist , New assignment , If it already exists , The original value will be overwritten

4. Delete array data

Because arrays are essentially variables , So you can go through “unset Array [ Subscript ]” Clear the corresponding array elements , Without subscript , Means to clear all data of the entire array .

unset array[1]
unset array

5. Slice and replace [ Variable substring ]

Arrays are also variables , Therefore, it is also suitable for the functional application of substring processing of variables explained above .

1) Slicing function

array=(1 2 3 4 5)
echo ${array[@]:1:3}

2 3 4 From the subscript for 1 Start intercepting the elements of , Take together 3 Array elements . For other usage, refer to the usage of variable substring

2) Replace

array=(1 2 3 1 1)   
echo ${array[@]/1/b}

b 2 3 b b Put... In the array 1 Replace with b, The original array has not been modified , and sed It's like . For other usage, refer to the usage of variable substring The calling method is ：${ Array name [@ or *]/ To find the character / Replace character } This operation does not change the original array

Two 、 Case study

1. Number of elements in the content Print array

• array=(1 2 3 4 4) && echo ${array[@]} 1 2 3 4 4
• echo ${#array[@]} 5
• echo ${array[1]} 2

By default, array subscripts are from 0 Start counting

2. for Loop print array

Use arrays and for The cycle will “i am oldboy my teacher is luogang” In this sentence , The number of characters is less than or equal to 6 Print out words of

• cat /server/scripts/d1.sh

#!/bin/bash
array=(i am oldboy my teacher is luogang)
for n in ${array[*]}
do
  if [ `echo $n|wc -L` -le 6 ]
    then
      echo $n
  fi
done
echo -----------------
for((i=0;i<${#array[*]};i++))
do
  if [ ${#array[i]} -le 6 ]
    then
      echo ${array[i]}
  fi
done

• sh /server/scripts/d1.sh