1. Shell Script
Assignment 1

2. Shell
It is called a "shell" because it hides the details of the underlying OS behind the shell's interface.
In the Unix operating system users can select which shell they want to use.
Example – Bourne Shell, C Shell etc.
Programming with shell – A shell script is a file that contains commands to be executed by the shell.

3. Shell Programming LogIn : Text Editor : ‘VI EDITOR’
Log in to any Linux machine of CS213 using PuTTy. Your program SHOULD RUN on any of those machines. 
Eg: rc16xcs213.managed.mst.edu
Text Editor : ‘VI EDITOR’
Open a file : vim fileneame.sh
Run a file :
sh filename.sh  (no need for execute permission)
chmod u+x filename (add execute permission)
filename

4. Basic Shell Programming
#![path to shell you want to use]
eg. #!/bin/sh: current script should be run by the Bourne shell
#: begins a comment
Variables:
Assignment: variablename=5 (no space between)
Usage: $variablename
Reading from the keyboard
read variablename

5. Basic Shell Programming
Pipe: |
eg. program 1 | program2 (send output of 1 to 2)
Redirection:
> : redirect standard output
eg. program1 > file1 (put output of program1 to file1)
>>: appends standard output
< : redirect standard input

6. Basic Shell Programming
Reading from a file:
cat filename | while read variablename do …
done
while read variablename
done < /directory/filename

7. Useful commands in shell
ls: display all file and directory names. Just like dir command in MS-dos.
mkdir: help to create the directory
cd: helps to change directory
pwd: helps to display current path
chmod: change mode of permission
echo: display the message
date: display the current date
who: output the currently logged in users’ info

8. Useful commands in shell
ps: reports a snapshot of current process, give details of all the user
touch: update the access and modification times of each file to current time
grep: searches the named input files (or standard input if no files are named) for lines containing a match to the given pattern
eg. grep aa file1
cat: create, append new data and display the contain of a file

9. Useful commands in shell
read: take input through keyboard
cmp: compares files byte by byte
cut: slice a file vertically, is used to output a column of data
eg. cat file1 | cut –f1 –d‘||’
awk: search for and process patterns in a file. When awk reads in a line, the first field can be referred to as “$1”, the second “$2”. The whole line is “$0”
eg. cat file1 | awk ‘{print $1}’

10. Logic of the Assignment 1
Read the option that the user wants to go with –
1 for printing ancestry tree of the shell script you are running
2 for printing online usernames
3 for printing what process any user is running
a separate option for quitting the program.
Execute the option that is chosen by the user
Example run:
Better to use “case” for the menu

11. Case Statement Syntax: case $variableName in pattern1) command ;;*)
esac

12. Part 1
Print the ancestry tree of the currently running process (i.e. your shell script). Print is like a tree.
3465 |
3464
2990
509 1

13. Hints:
Find out, store and print the current process ID and its parent process ID. You can use ps –ef (-ef for standard syntax), and awk to print the required field - procees ID, program name (optional).
Store all the process details (output of ps) in a file (say file1)
In an iterative loop, check if the PID field of any entry matches the parent ID. If so, print the PPID field of that entry, and continue the same search with this PPID until reach init()

14. Hints: currentProcessID=previous parentProcessID
While ( currentProcessID NOT equal to 1 )
If (currentProcessID IS equal to ProcessID) in file1
Print parentProcessID field of that entry from file1
currentProcessID  parentProcessID
End If
End while

15. Useful syntax using awk:
awk ‘{if(condition) statement}’
currentProcessID=$(awk ‘{if(currentID field matches ProcessID)print;}’ file1 | print parentProcessID field)

16. Part 2 Figure out which users are online (print only username)
Hints: only one command (who command in conjunction with the cut command)

17. Part 3
Figure out what processes any user is running (Print Process details, not only name or ID)

18. Hints:
Update the access and modification times of each file using touch command(optional)
Read and print the entire userlist
Prompt to select one particular user and read the selected user

19. Read and print entire userlist
Read who is online (who command)
While (read the users online)
var  assign the current user
either print the var directly or write var in file1….the 2nd option is preferred.
End of while
Print file1 (in case you have saved it in file1)

20. Get the list of currently online user
who | while read onlineuser do echo $onlineuser | cut –f1 –d‘ ’ >>userlist done

21. Print numbered list of online users
index=1 while read onlineuser do print “$index-$onlineuser” Like before, save $index $onlineuser in a new file Increase index by 1 done < userlist

22. Select to see particular user
Remove userlist
Read numbered user from newfile and select one user using input 1 or 2 or …
desireduser=$(open newfile | pattern match with $choice | cut the 2nd field as o/p)
Get the process details of desired user
ps –ef | grep $desireduser (you will get extra processes)
ps -ef | while read process
do compare username
Remove newfile

23. Notes:
When you execute the program, don’t forget to script your session in a file called mySession1.
Use the command: script mySession1.
This will store your sample run in the file mySession1.
After run, don’t forget to exit, which will save and commit this sample file.
Submit this file along with your solution in dropbox.

24. CS284 Program Submission Follow instructions on the class website:

25. Thanks
Any Questions?