Shell exercise -20

Question requirements

Write a greeting program that can output greetings to the user according to the current time of the system when it is executed. Assume that from midnight to noon is morning, noon to 6 pm is afternoon, and 6 pm to midnight is evening.

Refer to the answer

if [-a] and the meaning
#!/bin/bash
d=`date +%H`
 if [$d -ge 0 -a $d -lt 7 ]
then
 tag=1
elif [$d -ge 7 -a $d -lt 12 ]
 then
 tag=2
elif [$d -ge 12 -a $d -lt 18 ]
then
 tag=3
else
 tag= 4
fi

case $tag in
 1)
 echo "Good morning"
 ;;
 2)
 echo "Good morning"
 ;;
 3)
 echo "Good afternoon"
 ;;
 4)
 echo "Good evening"
 ;;
 *)
 echo "The script went wrong"
 ;;
esac

Question requirements

Write a shell script, A simple pop-up menu function is realized, and the user can select and execute the corresponding command from the keyboard according to the displayed menu item.

Refer to the answer

Prefer the second way
#!/bin/bash
PS3="Please input your choice(1-4): " 
select i in w ls pwd quit
do
 case $i in 
 w)
 w
 ;;
 ls)
 ls
 ;;
 pwd)
 pwd
 ;;
 quit)
 exit
 ;;
 *)
 echo "Please input 1-3."
 ;;
 esac
done

Reference answer 2

#!/bin/bash 
echo -e "1) w
2) ls
3) pwd
4) quit"
while :
do
read -p "Please input your choice(1- 4): "c
case $c in 
 1)
 w
 ;;
 2)
 ls
 ;;
 3)
 pwd
 ;;
 4)
 exit
 ;;
 *)
 echo "Please input 1-4." 
 ;;
esac
done

Question requirements

Write a shell script and check whether the specified user is logged in to the system every 5 minutes during execution , The user name is input from the command line. If the specified user has logged in, the related information will be displayed.

Reference answer

#!/bin/bash
while :
do
 if w|sed '1'd|awk'{print $1}'|grep -qw "$1"
 then
 echo "User $1 has logged into the system."
 exit
 fi
 sleep 300
done< /pre> 
Question requirements
 
First popularize a little common sense, we can use ps aux to view the PID of the process, and each PID will be generated in /proc. If the pid viewed is not in the proc, the process has been modified by someone, which means that the system has probably been passed. 
Please use the above knowledge to write a shell, and regularly check whether your system has been used by others
 
Refer to the answer
 
#!/bin/bash
pp=$ $
ps -elf |sed '1'd> /tmp/pid.txt
for pid in `awk -v ppn=$pp'$5!=ppn {print $4}' /tmp/pid .txt`
do
 if! [-d /proc/$pid ]
 then
 echo "There is no directory whose pid is $pid in the system. It needs to be checked."< br /> fi 
done
Question requirements
Find a way to merge every three lines of text into one line.
For example: 1.txt content
1
2
3
4
5
6
7
It should be after processing
 < pre>1 2 3
4 5 6
7 
Reference answer
#Wrap directly when encountering a line that is not divisible by three

#!/bin/bash
n=1
cat $1 |while read line 
do
 n1=$[$n%3]
 if [$ n1 -eq 0 ]
 then
 echo "$line"
 else
 echo -n "$line "
 fi
 n=$[$n +1]
done