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Shell Script advanced

One 、 To choice 、 Judge

1、 To choice if

if  Judge the condition  1 ; then
   Branch code with true condition 
elif  Judge the condition  2 ; then
   Branch code with true condition 
elif  Judge the condition  3 ; then
   Branch code with true condition 
else
   All of the above conditions are false branch codes 
fi

Judge by conditions , First encounter “ really ” When the conditions , Take its branches , And then end the whole if.

Case study 1

# Judge age 
#!/bin/bash
read -p "Please input your age: " age
if [[ $age =~ [^0-9] ]] ;then
    echo "please input a int"
    exit 10
elif [ $age -ge 150 ];then
    echo "your age is wrong"
    exit 20
elif [ $age -gt 18 ];then
    echo "good good work,day day up"
else
    echo "good good study,day day up"
fi

analysis ： Please enter age , First determine whether the input contains characters other than numbers , Yes , Just report a mistake ; No, , Continue to judge if it is less than 150, Is it greater than 18.

Case list 2

# Judge the score 
#!/bin/bash
read -p "Please input your score: " score
if [[ $score =~ [^0-9] ]] ;then
    echo "please input a int"
    exit 10
elif [ $score -gt 100 ];then
    echo "Your score is wrong"
    exit 20
elif [ $score -ge 85 ];then
    echo "Your score is very good"
elif [ $score -ge 60 ];then
    echo "Your score is soso"
else
    echo "You are loser"
fi

analysis ： Please enter the grade , First determine whether the input contains characters other than numbers , Yes , Just report a mistake ; No, , Continue to judge whether it is greater than 100, Is it greater than 85, Is it greater than 6.

2、 conditional case

case $name in;
PART1)
  cmd
  ;;
PART2)
  cmd
  ;;
*)
  cmd
  ;;
esac

Be careful ：case Support glob Style wildcard ：

Any length, any character
?: Any single character
[] ： Any single character in the specified range
a|b: a or b

Case list 1

# Judge yes or no
#!/bin/bash
read -p "Please input yes or no: " anw
case $anw in
[yY][eE][sS]|[yY])
    echo yes
    ;;
[nN][oO]|[nN])
    echo no
    ;;
*)
    echo false
    ;;
esac

analysis ： Please enter yes or no, answer Y/y、yes The various case combinations are yes; answer N/n、No The various case combinations are no.

Two 、 Four cycles

1、for

① for name in  list  ;do
   The loop body 
done
② for (( exp1; exp2; exp3 )) ;do
  cmd
done

exp1 Only once , Equivalent to the for It's embedded in the wall while.

③ Execution mechanism ：

• Assign elements in the list to “ Variable name ”; The loop body is executed once after each assignment ; Until the elements in the list are exhausted , The loop ends
• The representation of a list , Sure glob wildcard , Such as {1…10} 、*.sh ; You can also refer to variables , Such as ：seq 1 $name

Case study 1

# Find out （1+2+...+n） The sum of 
sum=0
read -p "Please input a positive integer: " num
if [[ $num =~ [^0-9] ]] ;then
    echo "input error"
elif [[ $num -eq 0 ]] ;then
    echo "input error"
else
    for i in `seq 1 $num` ;do
        sum=$[$sum+$i]
    done
    echo $sum
fi
unset zhi  

analysis ：sum The initial value is 0, Please enter a number , First determine whether the input contains characters other than numbers , Yes , Just report a mistake ; There is no judgment whether it is 0, Not for 0 Get into for loop ,i For the range of 1~ Number of inputs , Each cycle is sum=sum+i, The loop ends , The final output sum Value .

Case list 2

# Find out （1+2+...+100） The sum of 

for (( i=1,num=0;i<=100;i++ ));do
        [ $[i%2] -eq 1 ] && let sum+=i
done
echo sum=$sum

analysis ：i=1,num=0; When i<=100, Into the loop , if i÷2 Remainder =1, be sum=sum+i,i=i+1.

2、while

while  Cycle control conditions  ;do
   loop 
done

Cycle control conditions ; Before entering the cycle , Make a judgment first ; After each cycle, the judgment will be made again ; Condition is “true” , Then execute a cycle ; Until the condition test status is “false” End cycle .

Special Usage ( Traverse every line of the file )

while read line; do Control variable initialization 
   The loop body 
done < /PATH/FROM/SOMEFILE
 or cat /PATH/FROM/SOMEFILE | while read line; do
   The loop body 
done

Read... In turn /PATH/FROM/SOMEFILE Every line in the file , And assign the row to the variable line.

Case list 1

#100 The sum of all positive odd numbers within 
sum=0
i=1
while [ $i -le 100 ] ;do
if [ $[$i%2] -ne 0 ];then
    let sum+=i
    let i++
else
    let i++
fi
done
echo "sum is $sum"

analysis ：sum The initial value is 0,i The initial value of 1; Please enter a number , First determine whether the input contains characters other than numbers , Yes , Just report a mistake ; Not when i<100 when , Into the loop , Judge i÷2 Remainder If not for 0, Not for 0 Time is odd ,sum=sum+i,i+1, by 0,i+1; The loop ends , The final output sum Value .

3、until loop

unitl  The loop condition  ;do
   loop 
done

Entry conditions ： The cycle condition is true ; Exit conditions ： The cycle condition is false; Just in time with while contrary , So not often , use while Just go .

Case list 1

# monitor dsjprs user , Log in and kill 
until pgrep -u dsjprs &> /dev/null ;do
        sleep 0.5
done
pkill -9 -u dsjprs

analysis ： every other 0.5 Second scan , Until I found out dsjprs The user login , Kill the process , Exit script , Used to monitor user login .

4、select Loops and menus

select variable in list
do
   Loop body command 
done

① select Loops are mainly used to create menus , The menu items in numerical order will be displayed on standard error , And display PS3 Prompt , Waiting for user input

② The user enters a number in the menu list , Execute the corresponding command

③ User input is saved in built-in variables REPLY in

④ select It's an infinite loop , So remember to use break Command to exit the loop , Or use exit Press Command to terminate the script . You can also press ctrl+c Exit loop

⑤ select and Often with case A combination of

⑥ And for Circulation similar , It can be omitted in list, In this case, the position parameter is used

Case list 1

# generate menu , And display the selected price 
PS3="Please choose the menu: "
select menu in mifan huimian jiaozi babaozhou quit
do
        case $REPLY in
        1|4)
                echo "the price is 15"
                ;;
        2|3)
                echo "the price is 20"
                ;;
        5)
                break
                ;;
        *)
                echo "no the option"
        esac
done

analysis ：PS3 yes select Prompt , Automatically generate menus , choice 5break Exit loop .

3、 ... and 、 Some usage in circulation

1、 Loop control statement

continue [N]： Finish the second N This cycle of layers , And go straight to the next round of judgment ; The innermost layer is 1 layer

break [N]： Finish the second N Layer cycle , The innermost part is 1 layer

 example ：while CONDTITON1; do
  CMD1
if CONDITION2; then
  continue / break
fi
  CMD2
done

Case list 1

#① seek （1+3+...+49+53+...+100） And 
#!/bin/bash
sum=0
for i in {
    1..100} ;do
        [ $i -eq 51 ] && continue
        [ $[$i%2] -eq 1 ] && {
     let sum+=i;let i++; }
done
echo sum=$sum

analysis ： do 1+2+…+100 The cycle of , When i=51 when , Skip this cycle , But continue the whole cycle , The result is ：sum=2449

Case list 2

#② seek （1+3+...+49） And 
#!/bin/bash
sum=0
for i in {
    1..100} ;do
        [ $i -eq 51 ] && break
        [ $[$i%2] -eq 1 ] && {
     let sum+=i;let i++; }
done
echo sum=$sum

analysis ： do 1+2+…+100 The cycle of , When i=51 when , Out of the loop , The result is ：sum=625

2、 Cycle control shift command

effect

It is used to set the parameter list list Move left a specified number of times , The leftmost parameter is removed from the list , The next parameter continues to enter the loop

Case list 1

#① Create a specified number of users 
#!/binbash
if [ $# -eq 0 ] ;then
        echo "Please input a arg(eg:`basename $0` arg1)"
        exit 1
else
        while [ -n "$1" ];do
                useradd $1 &> /dev/null
                shift
        done
fi

analysis ： If there are no input parameters （ The total number of parameters is 0）, Prompt for errors and exit ; conversely , Into the loop ; If the first parameter is not a null character , Then create a user named after the first parameter , And remove the first parameter , Move the following parameter to the left as the first parameter , Until there's no first parameter , sign out .

Case list 2

#② Print right triangle characters 
#!/binbash
while (( $# > 0 ))
do
        echo "$*"
        shift
done

3、 Return value result

true  Always return to success 
: null command , Do nothing , Return the successful result 
false  Always return the wrong result 

Create infinite loops

while true ;do
   The loop body 
done

4、 The loop can be executed in parallel , Make scripts run faster

for name in  list  ;do
  {
    
   The loop body 
  }&
done
wait

Case list 1

# Search your own designated ip（ The subnet mask is 24 Of ） In segments of ,UP Of ip Address 
read -p "Please input network (eg:192.168.0.0): " net
echo $net |egrep -o "\<(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\>"
[ $? -eq 0 ] || ( echo "input error";exit 10 )
IP=`echo $net |egrep -o "^([0-9]{1,3}\.){3}"`
for i in {
    1..254};do
        {
    
        ping -c 1 -w 1 $IP$i &> /dev/null && \
        echo "$IP$i is up" 
        }&

done
wait

analysis ： Please enter a IP Address example 192.168.37.234, If the format is not 0.0.0.0 Then report an error and exit ; Right goes into the cycle ,IP The value of the variable is 192.168.37. i For the range of 1-254, parallel ping 192.168.37.1-154,ping This is the output IP by UP. Until the end of the cycle .

Four 、 Signal acquisition trap

trap '  Trigger command '  The signal , After the custom process receives the specified signal from the system , The trigger command will be executed , Instead of performing the original operation 
trap ''  The signal , Ignore the operation of the signal 
trap '-'  The signal , The operation of restoring the original signal 
trap -p, List custom signal operations 

The signal can 3 There are two ways to express ： The number of signals 2、 full name SIGINT、 abbreviation INT

Common signals :

1) SIGHUP:  Reread the configuration file without shutting down the process 
2) SIGINT:  Abort a running process ; amount to Ctrl+c
3) SIGQUIT:  amount to ctrl+\
9) SIGKILL:  Force to kill a running process 
15) SIGTERM ： Terminate a running process （ The default is 15）
18) SIGCONT ： Continue operation 
19) SIGSTOP ： Background sleep 
9  The signal , Force to kill , I can't catch it 

Case list 1

#① Print 0-9,ctrl+c Cannot terminate 
#!/bin/bash
trap 'echo press ctrl+c' 2
for ((i=0;i<10;i++));do
        sleep 1
        echo $i
done

analysis ：i=0, When i<10, Every sleep 1 second ,i+1, Capture 2 The signal , And implement echo press ctrl+c

Case list 2

#② Print 0-3,ctrl+c Cannot terminate ,3 Then recover , Can stop 

#!/bin/bash
trap '' 2
trap -p
for ((i=0;i<3;i++));do
        sleep 1
        echo $i
done
trap '-' SIGINT
for ((i=3;i<10;i++));do
        sleep 1
        echo $i
done

analysis ：i=0, When i<3, Every sleep 1 second ,i+1, Capture 2 The signal ;i>3 when , Release capture 2 The signal .

5、 ... and 、 Script knowledge

1、 Generate random characters cat /dev/urandom

# Generate 8 A random case letter or number  
cat /dev/urandom |tr -dc [:alnum:] |head -c 8

2、 Generate random number echo $RANDOM

 Determine scope  echo $[RANDOM%7]  Random 7 Number （0-6）
echo $[$[RANDOM%7]+31]  Random 7 Number （31-37）

3、echo Print color words

echo -e "\033[31malong\033[0m"  Show red along
echo -e "\033[1;31malong\033[0m"  Highlight red along
echo -e "\033[41malong\033[0m"  The background color of the display is red along
echo -e "\033[31;5malong\033[0m"  It's flashing red along
color=$[$[RANDOM%7]+31]
echo -ne "\033[1;${color};5m*\033[0m"  Show flashing random colors along

6、 ... and 、 significant Shell Script

1、9x9 Multiplication table

#!/bin/bash
for a in {
    1..9};do
        for b in `seq 1 $a`;do
                let c=$a*$b ;echo -e "${a}x${b}=$c\t\c"
        done
        echo    
done

2、 Color isosceles triangle

#!/bin/bash
read -p "Please input a num: " num
if [[ $num =~ [^0-9] ]];then
        echo "input error" 
else
        for i in `seq 1 $num` ;do
                xing=$[2*$i-1]
                for j in `seq 1 $[$num-$i]`;do
                        echo -ne " "
                done
                for k in `seq 1 $xing`;do
                        color=$[$[RANDOM%7]+31]
                        echo -ne "\033[1;${color};5m*\033[0m"
                done
                echo
        done
fi

3、 chess board

#!/bin/bash
red="\033[1;41m \033[0m"
yellow="\033[1;43m \033[0m"

for i in {
    1..8};do
        if [ $[i%2] -eq 0 ];then
                for i in {
    1..4};do
                        echo -e -n "$red$yellow";
                done
                echo
        else
                for i in {
    1..4};do
                        echo -e -n "$yellow$red";
                done
                echo 
        fi
done

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