Shell script for, while loop statements, price guessing games

1、for sentence

        （1）for structure
You need to specify a variable and a list of possible values , Repeat the same command sequence for each different value . Until the variable value is used up, the exit loop needs to be specified in advance
for  Variable name   in  Value list
do
        Command sequence
done

        （2） Application example

Add and delete accounts according to the name list
Specify employee list file users.txt, Repeat adding users , Set initialization password

        add to

vim /root/users.txt    （ List file used as a test ）
（ Add three users ）

LS    
QY
AS


vim uaddfor.sh

#!/bin/bash
A=$(cat /root/users.txt)
for B in $A
do
useradd $B
echo "000000" | passwd --stdin $B &> /dev/null    （ Set the password of each user to 000000）
done

chmod +x uaddfor.sh

./uaddfor.sh

tail -3  /etc/passwd    （ View new users ）

su  user name   （ Test login user ）

         Batch delete user's script

vim uaddfor.sh

#!/bin/bash
A=$(cat /root/users.txt)
for B in $A
do
        userdel -r $B &>/dev/null
done


chmod +x uaddfor.sh

./uaddfor.sh

tail -3  /etc/passwd    （ View the user again to delete ）

  according to IP Address list check host status
from ipadds.txt Read the... Of each server in the file IP Address , repeat ping Connectivity testing , And input according to the test results
Give the corresponding prompt message .

vim /root/ipadds.txt  ( List file used for testing )
192.168.1.10
192.168.1.20
192.168.1.30

vim ping.sh    ( Cycle through the scripts of each host )
#!/bin/bash
A=$(cat /root/ipadds.txt)
for IP in $A
do
        ping -c 3 -i 0.2 -W 3 $IP &> /dev/null
if [ $? -eq 0 ]
then
        echo "Host $IP is up."
else
        echo "Host $IP is down."
fi
done

chmod +x ping.sh

./ping.sh

2、while Loop statement

  It is required to control the number of cycles 、 The operands are numbered in numerical order 、 Repeat operation according to specific conditions . It's more suitable for
Another cycle -while sentence .
 

        （1）while Sentence structure
        while        Conditional test operation

do

        Command sequence

done

Use while Loop statement . There are two special condition test operations , namely true( really ) and false( false ). Use true do
As a condition . It means that the condition is always true . The command sequence within the loop will continue indefinitely , Unless the script is forced to terminate exit Statement exit script ); conversely , If you use false As a condition . Then the loop body will not be executed . These two special conditions can also
Use in if Conditional test of statement .

        （2）while Statement application example

Batch add and delete users with regular numbers
Increasing 20 Users
 

          add to

vim uaddwhile.sh

#!/bin/bash
A="user"
i=1                           （ Control the number of user name , The initial assignment is 1）
while [ $i -le 20 ]
do
useradd ${A}$i
echo "000000" | passwd --stdin ${A}$i &> /dev/null
let i++                        （ Equate to  i= expr $i +1  Make variable i The value of the increase 1）
done

chmod +x uaddwhile.sh

 ./uaddwhile.sh

grep "user" /etc/passwd | tail -3    （ Check whether the last three lines are incremented by 20 individual ）

        Delete

vim uaddwhile.sh

#!/bin/bash
A="user"
i=1
while [ $i -le 20 ]
do
userdel -r ${A}$i
let i++
done

./uaddwhile.sh

id user20

 It shows that if there is no such user, it will succeed 

          Price guessing game
A random price number is generated in advance by the script (0-999) As the actual price , Judge user guesses
Through environment variables RANDOM You can get a value less than 2 Of 16 A random integer to the power of
Calculate its relation with 1000 You can get the remainder of 0-999 Random price
You can guess repeatedly by true As a test condition while Cycle to achieve
End the cycle when the user guesses the actual price : The process of judging the predicted price and the actual price adopts if Statements for , Embedded
Set on while Circulating body ; Use variables to record the number of guesses .

vim jiage.sh

#!/bin/bash
PRICE=$(expr $RANDOM % 1000)
TIMES=0
echo " The actual price range of the goods is 0-999, Guess what it is ？"
while true
do
read -p " Please enter the number of prices you guessed ：" INT
let TIMES++
if [ $INT -eq $PRICE ]
then
        echo " Congratulations, you're right , The actual price is  $PRICE"
        echo " You guessed a total of $TIMES  Time "
        exit 0
elif [ $INT -gt $PRICE ]
then

        echo " It's too high !"
else
        echo " It's too low !"
fi
done

chmod +x jiage.sh

./jiage.sh        （ After executing the command, you will enter 0-999 Previous figures ）