Operating Systems – Shell Scripting (CS-2006)

Operating Systems lab work from Spring 2025 at FAST-NUCES – Bash scripts and C/C++ programs on processes, pipes, threads and CPU scheduling.

Live Links

What	Link
Repository	https://github.com/rohaan2802/OS_Shell_Script
Website (GitHub Pages)	https://rohaan2802.github.io/OS_Shell_Script/
Download (ZIP)	https://github.com/rohaan2802/OS_Shell_Script/archive/refs/heads/main.zip

Overview

This repository is my CS-2006 Operating Systems lab work from Spring 2025. There are two assignments.

Assignment 1 is mostly Bash: a disk cleanup helper, a file-utility menu, an application-usage tracker, a personal expense ledger, and a C string toolkit that runs each task in a grandchild process via fork and execlp.

Assignment 2 is C and C++: a multiplayer zombie survival game using processes and pipes, professor–student office hours with threads, a cricket lineup tool built around SJF, SRTF and Round Robin, four processes passing a message in a circle over unnamed pipes, and a three-level multilevel feedback queue scheduler.

The assignment briefs (PDF) are in each assignment folder, next to the code.

Course: CS-2006 – Operating Systems · Spring 2025 · FAST-NUCES · Roll: 22I-2327

What's Inside

Section	Folder	What's in it
Assignment 1 brief	assignment-01/assignment-01.pdf	The original Assignment 1 statement
Q01 Disk cleanup	assignment-01/q01-disk-cleanup	`q01-disk-cleanup.sh`
Q02 File utilities	assignment-01/q02-file-utilities	`q02-file-utilities.sh`
Q03 App usage	assignment-01/q03-app-usage	`q03-app-usage.sh`
Q04 String toolkit	assignment-01/q04-string-toolkit	`main_file.c` and five worker programs, plus a Makefile
Q05 Expense tracker	assignment-01/q05-expense-tracker	`q05-expense-tracker.sh`
Assignment 2 brief	assignment-02/assignment-02.pdf	The original Assignment 2 statement
Q01 Zombie survival	assignment-02/q01-zombie-survival	`zombie-survival.cpp`
Q02 Office hours	assignment-02/q02-office-hours	`office-hours.cpp`
Q03 Cricket scheduling	assignment-02/q03-cricket-scheduling	`cricket-scheduling.cpp`
Q04 Circular pipes	assignment-02/q04-circular-pipes	`circular-pipes.c`
Q05 MFQ scheduler	assignment-02/q05-mfq-scheduler	`mfq-scheduler.cpp`

Assignment 1

Q01 – Disk cleanup

A Bash script that walks $HOME and helps free space.

Lists the ten largest files (find, du, sort) and asks before deleting them.
Has a duplicate-file helper (MD5 checksums, with options to delete, hard-link or move the copies). In the default run that step is left commented, because a full scan of $HOME can take a while.
Clears cache under ~/.cache and common Firefox/Chrome cache folders. If you run it as root it also cleans /var/log and runs apt autoremove.
Suggests files not accessed in the last 10 days (-atime +10) and asks before deleting them.

This script can delete files. Do not run it on a machine you care about until you have read it. The largest-file and old-file steps ask first (Y/N, and rm -i). The cache clean does not ask.

cd assignment-01/q01-disk-cleanup
chmod +x q01-disk-cleanup.sh
./q01-disk-cleanup.sh

Q02 – File utilities

A menu-driven script. Every helper message is also appended to text_file.txt.

Show a file's permissions, then invert them (for example -rw-r--r-- becomes ---x-wx-wx) and show the result.
Search a file for a string. A dot in the pattern is treated as "any character", so c.t matches cat and cot.
Ask for N, then write dummy_file.txt with the first N lines of even-positioned files in the current directory and the last N lines of odd-positioned files (.sh files are skipped).
If a file's modification time is more than 24 hours old, touch it so the time becomes now.

cd assignment-01/q02-file-utilities
chmod +x q02-file-utilities.sh
./q02-file-utilities.sh

Sample (option 2, pattern c.t):

OUTPUT RESULT --->  The cat sat on the mat
OUTPUT RESULT --->  A cot is small

Q03 – Application usage

Tracks the focused X11 window every 10 seconds, appends a line to ~/app_usage.log, and prints a short usage report (minutes and seconds). If a listed "non-productive" app (chrome, gnome-terminal, nautilus, gedit, evince) stays in focus for a minute, the script sends a desktop notification and tries to close it with pkill.

Needs xdotool. notify-send is used for the warning.

sudo apt install xdotool libnotify-bin
cd assignment-01/q03-app-usage
chmod +x q03-app-usage.sh
./q03-app-usage.sh

Stop it with Ctrl+C. The limit is one minute, which is short on purpose so the block can be tested without waiting around.

Q04 – String toolkit (C)

You type one word. The parent writes it to input.txt, then for each task it double-forks and the grandchild runs a worker with execlp. Each worker reads input.txt and appends a line to output.txt (task, PID, result). Option 6 prints that file and exits.

Option	Worker	What it does
1	`reverse_str`	Reverse the string
2	`length_str`	Length
3	`ascii_add_2_str`	Add 2 to each character's ASCII value
4	`sort_str`	Sort the characters
5	`capitalize_str`	Uppercase

cd assignment-01/q04-string-toolkit
make
./main_file

Sample, input OperatingSystems:

TASK: REVERSE | PID: 51537 | RESULT: smetsySgnitarepO
TASK: FIND LENGTH | PID: 51539 | RESULT: 16
TASK: ADD 2 ASCII | PID: 51545 | RESULT: QrgtcvkpiU{uvgou
TASK: SORTING THE STRING | PID: 51553 | RESULT: OSaeegimnprsstty
TASK: CAPITALIZE THE STRING | PID: 51555 | RESULT: OPERATINGSYSTEMS

The input is a single token (scanf("%s")), so no spaces. The workers have to be in the same directory as main_file — make builds all of them there.

Q05 – Expense tracker

A small ledger stored in expenses.csv (date,category,amount). The menu lets you:

Add a row (category can be FOOD, BILLS, SHOPPING, INCOME, OTHER, or whatever you type).
Print a per-category total, overall expenses, monthly savings (income − expenses), and a warning if expenses go over the budget (default 100000, changeable from the menu).
Print the CSV.
Plot spending over time with gnuplot (income rows are left out of the graph). Optional: sudo apt install gnuplot.
Set a new budget.
Exit.

cd assignment-01/q05-expense-tracker
chmod +x q05-expense-tracker.sh
./q05-expense-tracker.sh

Sample, after a few entries (FOOD 250 + 400, BILLS 1200, INCOME 5000) and a budget of 1000:

                         FOOD = 650
                        BILLS = 1200
                       INCOME = 5000

                TOTAL EXPENSES  => 1850
                MONTHLY SAVINGS => 3150

        ALERT: BUDGET LIMIT EXCEEDED ..... !

Assignment 2

Q01 – Zombie survival

A terminal game. The parent is the game manager. Each player and each zombie is a child process and talks to the parent through a pipe. Players randomly move, attack, or find a weapon; zombies bite a random player. After five turns the higher score wins.

The number of zombies comes from the last four digits of my roll number: (2327 * 3) % 20 + 1, which is 2.

cd assignment-02/q01-zombie-survival
make
./zombie-survival

Q02 – Office hours

A professor thread and a student thread per person. Students take turns asking a question (question_start / question_done); the professor waits, answers, and only then is the next student allowed through (answer_start / answer_done). Shared flags are std::atomic, with no mutexes or semaphores, as the brief asked.

cd assignment-02/q02-office-hours
make
./office-hours

It will ask how many students. A run with one student looks like this:

PROFESSOR IS SLEEPING.....
STUDENT 1 ASKS A QUESTION......
STUDENT 1 HAS ASKED THE QUESTION.....
PROFESSOR STARTS ANSWERING STUDENT 1'S QUESTION.....
PROFESSOR HAS ANSWERED STUDENT 1'S QUESTION.....
STUDENT 1 RECEIVED THE ANSWER AND LEAVES......

Q03 – Cricket scheduling

You enter batsmen (name, matches, strike rate, average) and bowlers (name, matches, economy, wickets, average). For batting, SJF orders by strike rate and SRTF by average, then a predicted team score is printed. For bowling, SJF uses economy, SRTF uses wickets, and Round Robin rotates bowlers over a number of overs you choose.

cd assignment-02/q03-cricket-scheduling
make
./cricket-scheduling

Sample batting order (SJF, higher strike rate first):

Fakhar - STRIKE RATE: 132 - AVG SCORE: 35.5
Babar - STRIKE RATE: 125.5 - AVG SCORE: 45.2
Rizwan - STRIKE RATE: 118 - AVG SCORE: 42
PREDICTED TEAM SCORE: 122.70 RUNS

Q04 – Circular pipes

Four processes, A → B → C → D → A, connected by unnamed pipes. Process A starts with a message and logs it to log_A.txt. Each of B, C and D reads the message, lets you append a note, writes its own log file, and passes the result on. A prints the fully modified message when it comes back.

cd assignment-02/q04-circular-pipes
make
./circular-pipes

Sample:

PROCESS A, ENTER INITIAL MESSAGE:                  Hello OS
PROCESS B, ENTER THE MODIFICATION:                 - Processed by B
PROCESS C, ENTER MODIFICATION:                     - Processed by C
PROCESS D, ENTER MODIFICATION:                     - Processed by D
FINAL MODIFIED MESSAGE RECEIVED BY PROCESS A: Hello OS - Processed by B - Processed by C - Processed by D

Q05 – Multilevel feedback queue

A 3-level MFQ scheduler.

Queue 1: Round Robin, quantum 4. If a process is not done, it drops to queue 2.
Queue 2: Round Robin, quantum 8. If still not done, it drops to queue 3.
Queue 3: FCFS, runs to completion.

You enter N, then each process's PID, arrival time and burst time. The program prints turnaround time and waiting time.

cd assignment-02/q05-mfq-scheduler
make
./mfq-scheduler

Sample (the four-process example from the brief: bursts 20, 10, 15, 12):

PROCESS 1 -> TURNAROUND TIME: 54, WAITING TIME: 34
PROCESS 2 -> TURNAROUND TIME: 28, WAITING TIME: 18
PROCESS 3 -> TURNAROUND TIME: 53, WAITING TIME: 38
PROCESS 4 -> TURNAROUND TIME: 40, WAITING TIME: 28

Folder Structure

OS_Shell_Script/
├── assignment-01/
│   ├── assignment-01.pdf
│   ├── q01-disk-cleanup/
│   │   └── q01-disk-cleanup.sh
│   ├── q02-file-utilities/
│   │   └── q02-file-utilities.sh
│   ├── q03-app-usage/
│   │   └── q03-app-usage.sh
│   ├── q04-string-toolkit/
│   │   ├── Makefile
│   │   ├── main_file.c
│   │   ├── reverse_str.c
│   │   ├── length_str.c
│   │   ├── ascii_add_2_str.c
│   │   ├── sort_str.c
│   │   └── capitalize_str.c
│   └── q05-expense-tracker/
│       └── q05-expense-tracker.sh
├── assignment-02/
│   ├── assignment-02.pdf
│   ├── q01-zombie-survival/
│   │   ├── Makefile
│   │   └── zombie-survival.cpp
│   ├── q02-office-hours/
│   │   ├── Makefile
│   │   └── office-hours.cpp
│   ├── q03-cricket-scheduling/
│   │   ├── Makefile
│   │   └── cricket-scheduling.cpp
│   ├── q04-circular-pipes/
│   │   ├── Makefile
│   │   └── circular-pipes.c
│   └── q05-mfq-scheduler/
│       ├── Makefile
│       └── mfq-scheduler.cpp
├── screenshots/
├── assets/
│   ├── css/style.css
│   ├── js/main.js
│   ├── favicon.svg
│   └── og-image.png
├── index.html
├── LICENSE
└── README.md

How to Run

You need a Linux environment (or WSL) with Bash, gcc and g++. The C programs use POSIX calls (fork, pipe, execlp, pthreads), so they are meant to run on Linux, not plain Windows.

git clone https://github.com/rohaan2802/OS_Shell_Script.git
cd OS_Shell_Script

Each C/C++ folder has a Makefile:

cd assignment-01/q04-string-toolkit
make          # builds main_file and the five workers
./main_file
make clean    # removes the binaries and input.txt / output.txt

cd assignment-02/q01-zombie-survival
make && ./zombie-survival

The office-hours program is linked with -pthread (already in its Makefile).

Runtime files such as expenses.csv, output.txt and log_A.txt are produced when you run the programs. They are listed in .gitignore and are safe to delete.

Screenshots

1. Repository Folder Structure

2. Assignment 1 Brief

3. Disk Cleanup Script Output

4. File Utilities Main Menu

5. Invert File Permissions

6. Search with a Wildcard (c.t)

7. Copy First and Last N Lines

8. Update a Stale Modified Date

9. Application Usage Report

10. String Toolkit Menu

11. String Toolkit Results

12. Expense Tracker – Add and Summary

13. Budget Alert

14. Spending Trend Graph

15. Assignment 2 Brief

16. Zombie Survival Game

17. Office Hours (Professor and Student)

18. Cricket Batting Order (SJF)

19. Cricket Bowling Rotation (Round Robin)

20. Circular Pipe Message Passing

21. Multilevel Feedback Queue Stats

22. Website Home (Dark Theme)

23. Website Home (Light Theme)

24. Website on a Phone

25. Assignment 1 Section on the Website

License

The code I wrote is under the MIT License. The assignment PDFs belong to their instructors at FAST-NUCES and are here only for reference with this lab work. If you are an owner and want something removed, please open an issue.

Author

Mohammad Rohaan BS Computer Science – FAST-NUCES Roll no. 22I-2327

GitHub: @rohaan2802
Email: m.rohaanarshad@gmail.com

Name		Name	Last commit message	Last commit date
assets		assets
assignment-01		assignment-01
assignment-02		assignment-02
screenshots		screenshots
.gitattributes		.gitattributes
.gitignore		.gitignore
.nojekyll		.nojekyll
LICENSE		LICENSE
README.md		README.md
index.html		index.html

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