An Introduction to Operating Systems
Sharif University of technology
Fall 1385
Computer Assignment #2
Due: Tuesday 14/9/85
Note:
 All of assignments should be done by groups of one or two person! There is no
extra bonus for one-person groups.
 Ask us if you have any question or grey area about the assignment.
 All programs must be written in C/C++ (under Linux operating system of course!)
 You must use make to build your programs.
 You can find the Linux-Programming-Unleashed & Linux Advanced
Programming books in the http://ce.sharif.edu/courses/8586/1/ce424/index.php/section/resources/file/resources
 Please send your CA source code to ce424a@gmail.com before delivering it in
the following format:
Subject: Computer Assignment2
Body: first and last name and student ID of each member.
Attachment: Source code: family1_family2.zip
1. Bash and External commands:
Complete your bash in the previous assignment. Add the capability of executing
external commands and running the programs from your bash. Your bash should
support executing commands in background too. This means that when your bash
executes one command, it should be able to execute next command without waiting for
the termination of the process related to the first command.
Example of executing normally:
>> cmd arg1 arg2 … argn
>> cp –r /root/temp.txt
/home/SHMB/
Example of executing in background:
>> cmd arg1 arg2 … argn &
>> cp –r /root/temp.txt
/home/SHMB/ &
Note that if there is a common command among internal and external ones, you must
execute the internal command.
Hint: See manual version 3 of Linux for exec series commands (man 3 exec) and also see
the manual for fork command. Also take a look at Linux-Programming-Unleashed book,
chapter 11, System calls and library function section.
2. Introduction to IPC and Signaling.
Suppose that you want to add a history command to your bash. This means adding an
internal command (say history) which return last N commands that user executed. For
some reason we don’t want to save the history list in the bash process itself. Instead you
should write a program (say logger) which save this historical information and provides
some services too.
The whole thing you should do is, after each command entered by user, send a signal to
logger process to inform it you have a request. (If there is no logger process in the system
do nothing.) And then using one of IPC method such as pipe, shared memory, message
passing, etc (do not use socket programming) transform the command name to logger.
On the other hand the logger waits for a signal, after it receive the signal using IPC get
the history command and save it to some structure. For simplicity consider that you
should save some constant number of history commands.
History command:
This is a new internal command, you should add to your bash. It gets an argument (say
N) and return N last commands user requested. Like adding a new command to logger, at
first you should send a signal to logger process to inform it you have a request. This time
using IPC you should give the logger N, and then get the result and show them to user
Example:
myshell >> ls
.
..
temp1
temp2
myshell >> cd temp1
myshell >> history
error: there is no logger process running in the system.
myshell >> ls
.
..
shell.cpp
shell.h
logger
myshell >> ./logger
myshell >> chertopert
error: no such file or directory or command
myshell >> cd ..
myshell >> ls
.
..
temp1
temp2
myshell >> history 10
chertopert
cd
ls
history
myshell >> history 3
ls
history
history
Hint:
1. Since the bash itself execute logger program, it can identify logger’s PID simply.
2. See manual of Linux for fifo and signal commands (man fifo, man signal) and
also take a look at the Linux-Programming-Unleashed book.