First-Come-First-Serve (FCFS) and Shortest-Job-First (SJF) Scheduling Algorithms in Bash

Overview

This project demonstrates two classic CPU scheduling algorithms—First-Come-First-Serve (FCFS) and Shortest-Job-First (SJF)—implemented in Bash shell scripts. Both are non-preemptive algorithms used in operating systems. This repository is intended as an educational resource for students and anyone interested in learning about operating system concepts and shell scripting.

Why This Project?

As part of my journey learning about operating systems at university, I decided to implement classic scheduling algorithms using Bash. Implementing both FCFS and SJF in Bash helped me understand these algorithms and shell scripting fundamentals. I hope this project helps others who are learning as well!

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1. First-Come-First-Serve (FCFS) Scheduling

What is FCFS Scheduling?

• FCFS (First-Come-First-Serve) is a non-preemptive scheduling algorithm.
• Processes are executed in the order they arrive in the ready queue.
• It is simple to implement but can lead to the "convoy effect" where short processes wait for long ones to finish.

How the Script Works

• The script defines an array of burst times (the time each process needs on the CPU).
• It calculates the waiting time (WT) and turnaround time (TAT) for each process.
• It computes the average waiting and turnaround times.
• The results are displayed in a formatted table.

Script: First-Come-First-Serve.sh

Example Output

FCFS Scheduling:
Process	BT	WT	TAT
P[1]    6   0   6
P[2]    8   6   14
P[3]    7   14  21
P[4]    9   21  30

Average Waiting time = 10.25
Average Turnaround time = 17.75

How to Run FCFS Script

1. Make the script executable:

   chmod +x First-Come-First-Serve.sh

2. Run the script:

   ./First-Come-First-Serve.sh

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2. Shortest-Job-First (SJF) Scheduling

What is SJF Scheduling?

• SJF (Shortest-Job-First) is a non-preemptive scheduling algorithm.
• The process with the shortest burst time is executed first.
• It minimizes the average waiting time but requires knowledge of burst times in advance.

How the Script Works

• The script sorts the processes by their burst times.
• It calculates the waiting time (WT) and turnaround time (TAT) for each process after sorting.
• It computes the average waiting and turnaround times.
• The results are displayed in a formatted table.

Script: Shortest-Job-First.sh

Example Output

SJF Shortest Job First Scheduling
Processes	BT	WT	TAT
P[4]        3   0   3
P[1]        6   3   9
P[3]        7   9   16
P[2]        8   16  24

Average Turnaround Time =8.00
Average Waiting Time =7.00

How to Run SJF Script

1. Make the script executable:

   chmod +x Shortest-Job-First.sh

2. Run the script:

   ./Shortest-Job-First.sh

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Customizing the Scripts

• You can change the burst times by editing the bt array at the top of each script:

  bt=(6 8 7 9)  # FCFS example
  bt=(6 8 7 3)  # SJF example

• Add or remove values to simulate different process scenarios.

Educational Value

• Learn OS Concepts: Understand how basic scheduling works in operating systems.
• Practice Bash Scripting: See how arrays, loops, and arithmetic are handled in Bash.
• Experiment: Try modifying the scripts to implement other algorithms like Round Robin.

License

This project is open source and available under the MIT License.

Author

• Muhammad Usman Junaidy
• University Student | Operating Systems Enthusiast

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Feel free to fork, modify, and share! If you found this helpful or have suggestions, please open an issue or pull request.