Operating Systems and Computer Structures G2
Assignments
Overview
The purpose of the assignments is to introduce you to doing systems programming using the services supplied by the Operating System. This includes a shell program, a basic C program using the file system, a C program using multitasking, and a C program using remote procedure calls.Rather than a set of unrelated exercises, the intention this year is to build a realistic program at the end, with the earlier exercises forming components or simpler versions. The program (or rather, programs) will give a basic version of the type of problem that is commonly talked about today with the increase in use of the Internet. The programs will provide a ``jukebox'' on the Internet, where a set of sound files are stored on one server computer on the network. This server can be queried for a list of the sound files, or can be requested to send a file to another machine where it can be played using the local sound card.
Select an assignment:
Assignment 1
Due date
This assignment is due on midnight, Sunday 20 August.General
This assignment is to write a shell program. It makes use of three other programslist_sounds, fetch_sound,
xselect and xwarn, supplied by the lecturer.
The purpose is to get the list of sounds and display them so that they can be selected by the user. Once selected, a sound file is fetched and played.
To avoid repeated fetches across the network of the same sound files, each file should be `cached' locally so that it can be reused if needed.
The concepts that are used in this assignment are
- Shell programs using if..then..else statements and while... loops.
- Pipelines and I/O redirection.
- Regular expressions.
- Command substitution.
Supplied programs
The supplied programs are-
list_sounds -
This writes to standard output a list of lines, one per sound file.
Each line consists of a filename followed immediately with a colon `:'
(no white space), followed immediately by a description of the file.
For example,
petshop1:Petshop Boys ``Yesterday, when I was mad'' beatles1:Beatles ``Help'' beethoven5:Beethoven ``Fifth Symphony in C minor: First Movement'' The filename does not contain a colon `:'. The description does not contain the `{' or `}' characters. -
fetch_sound -
This program takes one argument, which should be the name of a file
from
list_sounds. If the file is valid, it writes to standard output the contents of the file. If successful, the exit code is 0, otherwise it is non-zero. -
xselect -
This program reads lines from standard input, and displays them as a list in
an X Window. When an item from the list is selected, it is written
to standard output.
If the item contains white space, it is surrounded by curly brackets `{...}'
as in
{Beatles ``Help''}. -
xwarn - This takes an arbitrary number of arguments, and displays them as a message in an error dialog box.
Specification
You should write a singlebash shell program. It should obtain
a list of sound files and their descriptions, and display the
descriptions as a list using xselect. When the user selects a
description, the corresponding sound file must be used.
A check should be
made as to whether or not the sound file is in the local cache,
that is, if it is
stored in directory .sounds relative to the current directory.
If it is, it should be used, otherwise it must be fetched across the
network. When fetched, it must also be stored in the cache.
The sound file will be used by playing it i.e. by writing it to
the device /dev/audio.
When the program exits, it must clean up the cache by removing the directory and all of its files.
Errors
If any errors occur, they should be reported using the commandxerror. If they are fatal errors, the program should
terminate, but otherwise continue.
Submission
Do not hand in a copy of the program on paper. Instead, hand it in electronically using the commandgive.
This command runs with two parameters.
The first parameter should be the string ``a1'' and the second should be the
name of the file containing the source of your shell program. For example,
if your shell file is called jukebox
give a1 jukebox
You may run give any number of times.
Each time you run give it replaces any
earlier submission of the assignment.
No record is kept of the number of submissions.
It does not alter your file in any way - it just makes a copy in a place
accessible only to the lecturer.
Other comments
If you want to use dialin access to work then some programs will need to be replaced. See here for more information.If you are running Linux, then you will need binary copies of some programs. See here for more information.