Assignment 1
 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 Programming
 LogIn :
 Log in to any Linux machine of CS213 using PuTTy. Your
program SHOULD RUN on any of those machines.
 Eg:
 Text Editor : ‘VI EDITOR’
 Open a file : vim
 Run a file :
sh (no need for execute permission)
chmod u+x filename (add execute permission)
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
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
Basic Shell Programming
 Reading from a file:
 cat filename | while read variablename
 while read variablename
done < /directory/filename
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
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
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
 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 $1}’
Logic of the Assignment 1
 Read the option that the user wants to go with –
 1 for printing ancestry tree of the shell script you are
 2 for printing online usernames
 3 for printing what process any user is running
 a separate option for quitting the program.
 Execute the option that is chosen by the user
 Example run:
 Better to use “case” for the menu
Case Statement
 Syntax:
Part 1
 Print the ancestry tree of the currently running
process (i.e. your shell script). Print is like a tree.
 Find out, store and print the current process ID and its
parent process ID. You can use ps –ef (-ef for standard
syntax), and awk to print the required field - procees
ID, program name (optional).
 Store all the process details (output of ps) in a file (say
 In an iterative loop, check if the PID field of any entry
matches the parent ID. If so, print the PPID field of
that entry, and continue the same search with this
PPID until reach init()
currentProcessID=previous parentProcessID
While ( currentProcessID NOT equal to 1 )
If (currentProcessID IS equal to ProcessID) in file1
Print parentProcessID field of that entry
from file1
currentProcessID  parentProcessID
End If
End while
Useful syntax using awk:
 awk ‘{if(condition) statement}’
 currentProcessID=$(awk ‘{if(currentID field matches
ProcessID)print;}’ file1 | print parentProcessID field)
Part 2
 Figure out which users are online (print only
 Hints: only one command (who command in
conjunction with the cut command)
Part 3
 Figure out what processes any user is running
(Print Process details, not only name or ID)
 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
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)
Get the list of currently online user
who | while read onlineuser
echo $onlineuser | cut –f1 –d‘ ’ >>userlist
Print numbered list of online users
while read onlineuser
print “$index-$onlineuser”
Like before, save $index $onlineuser in a new file
Increase index by 1
done < userlist
Select to see particular user
 Remove userlist
 Read numbered user from newfile and select one user
using input 1 or 2 or …
desireduser=$(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
 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.
CS284 Program Submission
 Follow instructions on the class website:
Any Questions?

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