Shell script case ---2

1） please ping Pass Baidu domain name 3 Time , Different information is output for success or failure .
Complete in three ways .

Mode one ：
The point to note here is , If 3 Tidu ping through ,&& It will take effect , That is, execute the following commands ,ping www.baidu.com ok
3 Once only once no ping through ,|| take effect , Will execute the following commands ,ping www.baidu.com error

#!/bin/bash
IP=www.baidu.com
ping -c3 $IP &>/dev/null && echo "ping $IP ok" || echo "ping $IP error"

Mode two ：
use if Statement completion non interactive ping website
Non interactive as follows ：

#!/bin/bash

# Defining variables 
ip=www.baidu.com

# only ping Three times without outputting anything 
ping -c3 $ip &>/dev/null

# Judge the execution result of the previous statement , If the execution is successful, it will be 0; It is 1
if [ $? -eq 0 ];then
  echo "$ip ok"
else
  echo "$ip error"
fi

Mode three ：
use if Statement completes interactive ping website
Interactive as follows ：

#!/bin/bash

# After executing the script , User input variables IP, And there are prompt statements 
read -p "please input network ip:" IP

# only ping Three times without outputting anything 
ping -c3 $IP &>/dev/null

# Judge the execution result of the previous statement , If the execution is successful, it will be 0; It is 1
if [ $? -eq 0 ];then
  echo "$IP ok"
else
  echo "$IP error"
fi

2） The meaning of the relevant parameters .
primary shell The script is as follows ：

[[email protected] scripts]# cat test.sh 
#!/bin/bash
echo " The first 3 A place is $3"
echo " The first 2 A place is $2"
echo " The first 1 A place is $1"
echo " All the parameters are ：$*"
echo " All the parameters are ：[email protected]"
echo " The number of parameters is ：$#"
echo " The current process PID yes ：$$"
echo " The current file name is ：$0"
echo '$4=' $4
echo '$5=' $5
echo '$*=' $*
echo '$$=' $#
echo '[email protected]=' [email protected]
echo '$$=' $$
echo '$0=' $0

The execution result of the script is as follows ：

[[email protected] scripts]# sh test.sh 1 2 3 4 5 
 The first 3 A place is 3
 The first 2 A place is 2
 The first 1 A place is 1
 All the parameters are ：1 2 3 4 5
 All the parameters are ：1 2 3 4 5
 The number of parameters is ：5
 The current process PID yes ：76280
 The current file name is ：test.sh
$4= 4
$5= 5
$*= 1 2 3 4 5
$$= 5
[email protected]= 1 2 3 4 5
$$= 76280
$0= test.sh

About single quotation marks and double quotation marks

 Single quotation marks --- What you see is what you get --- Strong citation --- For Strings 
 Double quotes --- Analysis of variables --- Weak reference --- For Strings 

3） Check disk usage , If exceeded 10%, Then input the results into the file /tmp/Disk_Free.txt in ; Otherwise output content “ The disk is currently in good condition ”

#!/bin/bash

# First use df -h Check disk usage 
# Reuse grep Match to the row of the root partition 
# Then use awk Find the disk usage and filter out the percent sign , To facilitate comparison 
Disk_Free=$(df -h|grep /$|awk '{print $(NF-1)}'|awk -F '%' '{print $1}')

# Compare the results with 10 Compare , The result here is as echo Output content , Variables should be enclosed in braces 
if [ $Disk_Free -gt 10 ];then
  echo "disk use is:${Disk_Free}%" >> /tmp/Disk_Free.txt
else
  echo "disk use is ok,now is ${Disk_Free}%" >>/tmp/Disk_Free.txt
fi

4） Output Linux System related information .

[[email protected] scripts]# cat test.sh 
#!/bin/bash
System=$(hostnamectl|grep System|awk -F ':' '{print $2}')
Kernel=$(hostnamectl|grep Kernel|awk -F ':' '{print $2}') 
virtua=$(hostnamectl|grep Virtua|awk -F ':' '{print $2}')
st_hos=$(hostnamectl|grep host|awk -F ':' '{print $2}')
    
echo " operating system ：$System" >>/tmp/info.txt
echo " system kernel ：$Kernel" >>/tmp/info.txt
echo " Virtual platform ：$virtua" >>/tmp/info.txt
echo " Static host ：$st_hos" >>/tmp/info.txt

#CPU Load condition 
cpu_load1=$(w|grep load|awk -F '[, ]+' '{print $(NF-2)}')
cpu_load5=$(w|grep load|awk -F '[, ]+' '{print $(NF-1)}')
cpu_load15=$(w|grep load|awk -F '[, ]+' '{print $NF}')
echo "CPU1 The minute load is ：$cpu_load1" >> /tmp/info.txt
echo "CPU5 The minute load is ：$cpu_load5" >> /tmp/info.txt
echo "CPU15 The minute load is ：$cpu_load15" >> /tmp/info.txt

echo "==================$(date +%F)=================" >>/tmp/info.txt

5-1） use for loop , Input user prefix and number of users interactively , The user password is uniformly set to 123, Mass create users .

[[email protected] scripts]# vim test.sh 
#!/bin/bash

read -p " Please enter the number of users :" num
read -p " Please enter a prefix ："  pre

for i in $(seq $num);do
    username=$pre$i
    useradd $username &> /dev/null
    echo 123|passwd --stdin $username &> /dev/null
    if [ $? -eq 0 ];then
        echo "user $username create ok"
    fi
done

To delete the above users in batch , a line Linux Command is enough .
（ Suppose you create 10 Users ,boy1 boy2 boy3 … boy10）

for i in boy{
    1..10};do userdel $i;done

5-2） On the basis of the first question , First, judge whether the number of created users entered is a number

[[email protected] scripts]# cat test.sh 
#!/bin/bash
read -p " Please enter the number of users :" num
if [[ ! $num =~ ^[0-9]+$ ]];then
    echo " error , Please enter a number "
    exit 1
fi

read -p " Please enter a prefix ："  pre

for i in $(seq $num);do
    username=$pre$i
    useradd $username &> /dev/null
    echo 123|passwd --stdin $username &> /dev/null
    if [ $? -eq 0 ];then
        echo "user $username create ok"
    fi
done

5-3） On the basis of the second question , Determine whether the prefix of the user name is a letter , And you can have countless opportunities to try and make mistakes .

[[email protected] scripts]# cat test.sh 
#!/bin/bash
read -p " Please enter the number of users :" num

while true
do
    if [[ $num =~ ^[0-9]+$ ]];then
        break
    else
        echo " error , Please enter a number "
        read -p " Please enter the number of users :" num
    fi
done

read -p " Please enter a prefix ：" pre

while true
do
    if [[ $pre =~ ^[a-Z]+$ ]];then
        break
    else
        echo " error , Please enter Pinyin "
        read -p " Please enter a prefix ：" pre
    fi
done

for i in $(seq $num);do
    username=$pre$i
    useradd $username &> /dev/null
    echo 123|passwd --stdin $username &> /dev/null
    if [ $? -eq 0 ];then
        echo "user $username create ok"
    fi
done