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Functions and arrays of shell scripts

2022-07-04 01:02:00 【Wozkid】

One 、shell function

1.1 Function function

1. A statement block is defined as a function approximately equal to an alias , Defined function , Rereference function

2. Encapsulated, reusable, functional code

1.2 The basic format of the function

      
      
       
        Format 1：
       
       
function  Function name  {
       
       
command
       
       
}        ### This is a standard way of writing 
       
       

       
       
 Format 2：
       
       
 Function name （）{     
       
       
command
       
       
}        ### Most commonly used because of the most concise 
      
      
      
      
       
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1.3 Function call

Directly define the code block of the function in the script and write the function name to complete the call

Example ：

      
      
       
       [[email protected] ~]# vim kk.sh
       
       
#!/bin/bash
       
       

       
       
function f {             ### Define a function called f
       
       
echo "hello world!"    ### The function is to print “hello world!”
       
       

       
       
}
       
       
f    ### Writing the function name directly will run the code in the function 
       
       

       
       
[[email protected] ~]# sh kk.sh 
       
       
hello world!
      
      
      
      
       
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notes ： Function name must be unique , If you define a , Use the same name to define , The second will override the function of the first , There are results you don't want , So be careful not to duplicate your name here ！

      
      
       
       [[email protected] ~]# vim kk.sh
       
       
#!/bin/bash
       
       

       
       
f1 () {
       
       
echo "hello"
       
       

       
       
}
       
       

       
       
f2 () {
       
       
echo "world"
       
       
}
       
       

       
       
f3 () {
       
       
echo "$(f1) $(f2)"
       
       
}
       
       

       
       
f3
       
       

       
       

       
       
[[email protected] ~]# sh kk.sh 
       
       
hello world
      
      
      
      
       
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1.4 The return value of the function

return Represents the exit function and returns an exit value , You can use $? The variable represents the value

The principle of using functions ：

1. Take the return value as soon as the function ends , because $? Variable returns only the exit status code of the last command executed ;

2. Exit status code must be 0~255, When exceeded, the value will be divided by 256 Remainder .

Example ：

      
      
       
       [[email protected] ~]# vim kk.sh
       
       
#!/bin/bas
       
       

       
       
user () {
       
       
if [ $USER = root ]
       
       
then
       
       
        echo " This is the administrator user "
       
       
else
       
       
        echo " This is not an administrator user "
       
       
return 1
       
       
fi
       
       
}
       
       

       
       
user
       
       

       
       
[[email protected] ~]# sh kk.sh 
       
       
 This is the administrator user 
       
       
[[email protected] ~]# echo $?
       
       
0
       
       

       
       
[[email protected] ~]# su lu
       
       
[[email protected] ~]$ sh kk.sh
       
       
 This is not an administrator user 
       
       
[[email protected] ~]$ echo $?
       
       
1
      
      
      
      
       
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1.5 Arguments to functions

stay Shell in , You can pass parameters to a function when you call it . Inside the body of the function , adopt $n To get the value of the parameter , for example ,$1 Represents the first parameter ,$2 Represents the second parameter … That is to use position parameters to realize parameter transfer .

Example ：

Sum two numbers

      
      
       
       [[email protected] ~]# vim kkk.sh
       
       
#!/bin/bash
       
       

       
       
sum () {
       
       
read -p " Please enter the first number ：" NUM1
       
       
read -p " Please enter the second number ：" NUM2
       
       
echo " The two numbers you entered are : $NUM1  and  $NUM2"
       
       
sum=$((NUM1+NUM2))
       
       
echo " The sum of two numbers is ：$sum"
       
       
}
       
       
sum
       
       

       
       
[[email protected] ~]# sh kkk.sh 
       
       
 Please enter the first number ：6
       
       
 Please enter the second number ：66
       
       
 The two numbers you entered are : 6  and  66
       
       
 The sum of two numbers is ：72
      
      
      
      
       
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Case study ：

Factorial

      
      
       
       [[email protected] ~]# vim kkk.sh
       
       
#!/bin/bash
       
       

       
       
jc () {
       
       
che=1
       
       
for i in {1..5}
       
       
do
       
       
let che=$i*$che
       
       
done
       
       
echo $che
       
       
}
       
       

       
       
jc
       
       

       
       
[[email protected] ~]# sh kkk.sh 
       
       
120
       
       

       
       

       
       

       
       
 Optimized version ： Calculate the factorial of several orders according to the demand 
       
       

       
       
[[email protected] ~]# vim kkk.sh
       
       
#!/bin/bash
       
       
jc () {
       
       
che=1
       
       
read -p " Please enter the factorial you want to calculate ：" num
       
       
for i in `seq $num`
       
       
do
       
       
let che=$i*$che
       
       
done
       
       
echo $che
       
       
}
       
       

       
       
jc
       
       

       
       

       
       
[[email protected] ~]# sh kkk.sh 
       
       
 Please enter the factorial you want to calculate ：5
       
       
120
       
       
[[email protected] ~]# sh kkk.sh 
       
       
 Please enter the factorial you want to calculate ：6
       
       
720
      
      
      
      
       
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1.6 Local and global variables

Variables defined in the script or not declared as local variables in the function body are global variables , It means at present shell The environment recognizes

If you need this variable to be used only in the function, you can use... In the function local Keyword declaration , In this way, even if there is a variable with the same name outside the function, it doesn't matter , It does not affect the use in the function body

If it is to use source If you execute the script, you can see the difference

To call a command externally, you need to first source once . And then call the function. , Then call the variable in the function

      
      
       
       [[email protected] ~]# a=hello
       
       

       
       
[[email protected] ~]# vim kkkk.sh
       
       
#!/bin/bash
       
       

       
       
f1 () {
       
       
echo $a
       
       
a=world
       
       
echo $a
       
       
}
       
       

       
       
f1
       
       

       
       
[[email protected] ~]# source kkkk.sh  ### use source Execute the script , Will find a The value of 
       
       
hello
       
       
world
       
       
[[email protected] ~]# echo $a
       
       
world
       
       

       
       
 Use... In the body of a function local Defining variables a Value 
       
       
[[email protected] ~]# vim kkkk.sh
       
       
#!/bin/bash
       
       

       
       
f1 () {
       
       
echo $a
       
       
local a=world
       
       
echo $a
       
       
}
       
       

       
       
f1
       
       

       
       
[[email protected] ~]# source kkkk.sh   ### Execute script discovery a The value of 
       
       
world
       
       
world
      
      
      
      
       
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1.7 Recursion of a function

The function itself calls itself

List the files in the directory , The catalogue is shown in blue , The file displays hierarchical relationships

      
      
       
       [[email protected] ~]# vim kkkk.sh
       
       

       
       
#!/bin/bash
       
       
list(){
       
       
for i in $1/*
       
       
do
       
       
        if [ -d $i ];then
       
       
        echo -e "\e[34m$i\e[0m"
       
       
        list $i " $2"
       
       
        else
       
       
        echo "$2$i"
       
       
fi
       
       
done
       
       
}
       
       
list $1 $2
       
       

       
       
[[email protected] ~]# sh kkkk.sh /home
       
       
/home/kk
       
       
 /home/kk/*
       
       
/home/lu
       
       
/home/lu/ public 
       
       
  /home/lu/ public /*
       
       
/home/lu/ Templates 
       
       
  /home/lu/ Templates /*
       
       
/home/lu/ video 
       
       
  /home/lu/ video /*
       
       
/home/lu/ picture 
       
       
  /home/lu/ picture /*
       
       
/home/lu/ file 
       
       
  /home/lu/ file /*
       
       
/home/lu/ download 
       
       
  /home/lu/ download /*
       
       
/home/lu/ music 
       
       
  /home/lu/ music /*
       
       
/home/lu/ desktop 
       
       
  /home/lu/ desktop /*
      
      
      
      
       
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Two 、 Array

2.1 shell Definition of array

1. You can store multiple values in an array .Bash Shell Only one-dimensional arrays are supported （ Multidimensional arrays are not supported ）

2. The subscripts of array elements are 0 Start .

3.Shell Arrays are represented in parentheses , Element use " Space " Symbol split

4. stay shell In the sentence , Use 、 When traversing an array , The array format should be written as ${arr[@]} or ${arr[*]}

An array is a collection of data of the same type , It opens up a continuous space in memory , Usually used together with recycling

The classification of arrays ：

Normal array : Direct definition without declaration , Subscript index can only be an integer

Associative array : Need to use declare -A Statement Otherwise the system doesn't recognize , The index can be a string

2.2 How to define an array

      
      
       
        The first one is : Directly enclose the elements to be added to the array in parentheses , Separate... With spaces in the middle 
       
       
num= ( 11 22 33 44 ) 
       
       

       
       
${ #num}  Shows the length of the string 
       
       
 Array name =(value0 value1 value2)
       
       
 The second kind : Precisely define a value for each subscript index and add it to the array , Index numbers can be discontinuous 
       
       
num= ( [ 0 ]=55 [ 1 ]=66 [ 2 ]=77  [ 4 ]=88)
       
       

       
       
 Array name =( [ 0 ]=value  [ 1 ]=value  [  2 ]=value. . . )
       
       
 The third kind of : First assign all the elements to be added to the array to a variable , Then reference this variable and add it to the array .
       
       
list="11 12 13 14"
       
       
 
       
       
num=($list)
       
       

       
       
 List name ="value0 value1 value2..."
       
       
 Array name =($ List name )
       
       

       
       
 A fourth ： Define according to the subscript 
       
       
 Array name [0]="11"
       
       
 Array name [1]="22"
       
       
 Array name [2]="33"
       
       
 
       
       
 Array name [0]="value"
       
       
 Array name [1]="value"
       
       
 Array name [2]="value"
      
      
      
      
       
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2.3. Common usage of array

1. Gets the length of the array

      
      
       
       [[email protected] ~]# ar_number=(10 20 30 40 50)
       
       
[[email protected] ~]# ar_length=${#ar_number[*]}
       
       
[[email protected] ~]# echo $ar_length
       
       
5
       
       
[[email protected] ~]# ar_number=(10 20 30 40 50)
       
       
[[email protected] ~]# ar_length=${#ar_number[@]}
       
       
[[email protected] ~]# echo $ar_length
       
       
5
      
      
      
      
       
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2. Array element traversal

      
      
       
       [[email protected] ~]# vim kkkk.sh
       
       

       
       
#!/bin/bash
       
       
arr=(1 2 3 4 5 6)
       
       
for i in ${arr[*]}  ### or   for i in ${arr[@]}
       
       
do
       
       
echo $i
       
       
done
       
       

       
       
[[email protected] ~]# sh kkkk.sh 
       
       
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3. Element slice

      
      
       
       [[email protected] ~]# arr=(1 2 3 4 5 6)
       
       
[[email protected] ~]# echo ${arr[*]}
       
       
1 2 3 4 5 6
       
       
[[email protected] ~]# echo ${arr[*]:2:3}
       
       
3 4 5
       
       
[[email protected] ~]# echo ${arr[*]:2:4}
       
       
3 4 5 6
       
       
[[email protected] ~]# echo ${arr[*]:0:5}
       
       
1 2 3 4 5
      
      
      
      
       
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4. Array element replacement

      
      
       
        A temporary replacement 
       
       
[[email protected] ~]# arr=(1 2 3 4 56 7 8)
       
       
[[email protected] ~]# echo ${arr[*]}
       
       
1 2 3 4 56 7 8
       
       
[[email protected] ~]# echo ${arr[*]/56/5 6}
       
       
1 2 3 4 5 6 7 8
       
       
[[email protected] ~]# echo ${arr[*]}
       
       
1 2 3 4 56 7 8
       
       

       
       
 Permanently replace 
       
       
[[email protected] ~]# arr=(1 2 3 4 56 7 8)
       
       
[[email protected] ~]# echo ${arr[@]}
       
       
1 2 3 4 56 7 8
       
       
[[email protected] ~]# arr=(${arr[@]/56/5 6})
       
       
[[email protected] ~]# echo ${arr[@]}
       
       
1 2 3 4 5 6 7 8
      
      
      
      
       
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5. Array delete

      
      
       
        Delete the entire array 
       
       
[[email protected] ~]# arr=(1 2 3 4 56 7 8)
       
       
[[email protected] ~]# echo ${arr[@]}
       
       
1 2 3 4 56 7 8
       
       
[[email protected] ~]# unset arr
       
       
[[email protected] ~]# echo ${arr[@]}
       
       

       
       
[[email protected] ~]# 
       
       

       
       
 Delete the elements in the array 
       
       
[[email protected] ~]# arr=(1 2 3 4 5 6 7 8)
       
       
[[email protected] ~]# echo ${arr[@]}
       
       
1 2 3 4 5 6 7 8
       
       
[[email protected] ~]# unset arr[7]
       
       
[[email protected] ~]# echo ${arr[@]}
       
       
1 2 3 4 5 6 7
      
      
      
      
       
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3、 ... and 、 Bubble sort

1. Definition ：

It's like a bubble rising , Will move the data in the array from small to large or from large to small

2. The basic idea ：

The basic idea of bubble sorting is to compare the values of two adjacent elements , Exchange element values if conditions are met , Move the smaller elements to the front of the array , Move large elements to the back of the array ( That is, to exchange the positions of two elements ), So the smaller elements rise from the bottom to the top like bubbles

3. Algorithm ideas ：

The bubble algorithm is implemented by a two-layer loop , The external loop is used to control the number of sorting rounds , Generally, the length of the array to be sorted minus 1 Time , Because there's only one array element left in the last loop , There's no need to compare , At the same time, the array has finished sorting . The inner loop is mainly used to compare the size of each adjacent element in the array , To determine whether to swap positions , The number of comparisons and exchanges decreases with the number of sorting rounds

4. Bubble sort case ：

      
      
       
       #!/bin/bash
       
       
# Defining variables 
       
       
ar=(90 30 60 20 70 10)
       
       
echo " Before ordering ：${ar[*]}"
       
       
lt=${#ar[*]}
       
       
# Define the number of comparison rounds , The number of rounds is the length of the array -1, from 1 Start 
       
       
for ((i=1;i<$lt;i++))
       
       
do
       
       
        # Confirm the position of the comparison element , Compare adjacent elements , Larger move back , The number of comparisons decreases with the number of rounds 
       
       
        for ((l=0;l<$lt;l++))
       
       
        do
       
       
        # Define the value of the first element 
       
       
        first=${ar[$l]}
       
       
        # Define the value of the second element 
       
       
        k=$[$l+1]
       
       
        two=${ar[$l]}
       
       
        # If the first element is larger than the second, swap positions 
       
       
        if [ $first -gt $two ]
       
       
        then
       
       
        # Save the first element in a temporary variable 
       
       
        temp=$first
       
       
        # Assign the value of the second element to the first element 
       
       
        ar[$l]=$two
       
       
        # Assign a temporary variable to the second element 
       
       
        ar[$k]=$temp
       
       
        fi
       
       
        done
       
       
done
       
       
echo " After ordering ：${ar[*]}"
      
      
      
      
       
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