Project 1: Operating System

Project 1
CS-UH 3010: Operating System

The objective of this assignment is to become familiar with the use and programming in the
Linux Operating System environment. In this project, you will create an application which is
a simplified version of the UNIX SHELL using C/C++. This is going to be an individual
project, not a group project.
Your Task
Your task is to create an application called myshell to parse command line input from the user
and execute it if it is a built-in command. All command line input that user enters should
be recorded in the history file. You also need to implement shell variables which need to be
exported to your application through command line. You will implement the following built-in
commands.
• pwd - print name of current/working directory.
• cd - change the current directory.
• export - names of exported shell variables.
• history - display the command history list with line numbers.
• exit - free all space allocated gracefully and exit the application.
Project Requirements
• Your task is to create an application to parse command line input from the user and to
build the argv data structure in the form expected in any C/C++ main program. Input
line is separated by space as given below. [5pts]
identifier [identifier [identifier]]
• If it is a builtin command execute it, otherwise your program should search the directory
system in the order specified by the PATH variable for a file with the same name as the
first identifier and display the full path of the command and argument(s) passed. [10 pts]
• All path variables need to be exported to your application using export command. Variable
name PATH should be exported by default in your application but the user should be
able to modify it using export the command [20 pts]
• Application should record the command line inputs from the users and append it to the
history file. On every invocation of your application, you should be able to see the content
from history by using built-in command history. [20 pts]
• If the user types exit then free all space allocated gracefully, close all open file descriptors
and exit the application. [3 pts]
• Your application can change the current directory using built-in cd command and you can
verify it using pwd command. [7 pts]
• If the command is starting with the ! symbol and followed by a number then your program
needs invoke the line of command from the history file [10 pts]
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Procedural Matters
• Your program is to be written in C++ or C and must run on the NYUAD Linux (CentOS)
Server M-DCLAP-P302-CSD.abudhabi.nyu.edu(secure port: 4410)
eg:- ssh -p 4410 nr83@M-DCLAP-P302-CSD.abudhabi.nyu.edu
• You will have to first submit your project electronically and subsequently, demonstrate
your work.
• Nabil Rahiman (nr83@nyu.edu) will be responsible for answering questions as well as
reviewing and marking the assignment.
What you Need to Submit
• A directory that contains all your work including source, header, Makefile, etc.
• The program needs to be properly commented.
• All the above should be submitted in the form of a tar or zip file bearing your name (for
instance NabilRahimanProj1.tar).
• Submit the above tar/zip-ball using NYU classes
Grading Scheme
Aspect of Programming Assignment Marked Total Grade 100 pts
Quality in Code Organization and Modularity 8pts
Addressing All Requirements 75pts
Use of Makefile and Separate Compilation 5pts
Properly Commented Code 5pts
Handling unexpected termination 7pts
Noteworthy Points
• You have to use separate compilation in the development of your program.
• Although it is understood that you may exchange ideas on how to make things work and
seek advice from your fellow students, sharing of code is not allowed.
• If you use code that is not your own, you will have to provide appropriate citation (i.e.,
explicitly state where you found the code). Otherwise, plagiarism questions may ensue.
Regardless, you have to fully understand what and how such pieces of code do.
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Sample Program Output
$$./myshell
history

ls
command not found

export
PATH=


export PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
export
PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

ls -l -a
ls is an external command (/bin/ls)
command arguments:
cd h1

pwd
/home/test1/h1
cd h2/h3

pwd
/home/test1/h1/h2/h3

history
1 history
2 ls
3 export
4 export PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
5 export
6 ls -l -a
7 cd h1
8 pwd
9 cd h2/h3
10 pwd
11 history
export JAVA_PATH=/home/test/java/bin

export
PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
JAVA_PATH=/home/test/java/bin
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history
1 history
2 ls
3 export
4 export PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
5 export
6 ls -l -a
7 cd h1
8 pwd
9 cd h2/h3
10 pwd
11 history
12 export JAVA_PATH=/home/test/java/bin
13 export
14 history

!2
ls is an external command (/bin/ls)
command arguments:
-l
-a
exit
Your program terminates here. Invoke program again to verify you recorded the command
history in history file.
$$./myshell
history
1 history
2 ls
3 export
4 export PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
5 export
6 ls -l -a
7 cd h1
8 pwd
9 cd h2/h3
10 pwd
11 history
12 export JAVA_PATH=/home/test/java/bin
13 export
14 history
15 exit
16 history
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Additional Materials
Table 1: Some Useful system calls
open(2) open and possibly create a file
access(2) check real user’s permissions
read(2) read from a file descriptor
write(2) write to a file descriptor, for details type: man 2 write
getwd(3) get current working directory
chdir(2) change working directory
exit(2) terminate the program
Table 2: Some Useful gdb commands
break foo Breakpoint at function foo
break fees.c:39 Breakpoint at line 39
run Run the program util breakpoint is hit
cont Continue running (after hitting a breakpoint)
bt Print a back trace (BT) of the function call stack
print i Print value of local variable i
print &i Print address of variable i
info frame Print information about the current stack frame
Table 3: Unix Development Tools
gcc/g++ GNU C/C++ compiler
gbd GNU debugging tool
strace system call tracer
vim Text command line editor
make GNU make utility to maintain groups of programs
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