Mini Unix Shell (C)

A Unix-like shell implementation in C that supports process execution, pipes, signals, and job control.

This project was developed as part of an Operating Systems course and demonstrates how command interpreters interact with the OS using low-level system calls.

Overview

This project implements a simplified command-line interpreter (shell) similar to traditional Unix shells.

The shell parses user input, executes commands using fork/exec, manages foreground and background processes, and supports features such as pipes, signals, and command history.

The implementation demonstrates how operating systems manage processes and how user-level programs interact with OS services.

Features

Command Execution

• Execute external programs using fork() and execvp()
• Support for foreground and background execution (&)
• Built-in cd command

Process Management

• Track running processes
• Display process list (procs)
• Process states: RUNNING / SUSPENDED / TERMINATED

Signal Handling

• Send signals to processes:
  • wakeup (SIGCONT)
  • suspend (SIGTSTP)
  • nuke (SIGINT)
• Proper signal propagation and handling

Pipes and Redirection

• Support for single pipe (|) between commands
• Input/output redirection (<, >)
• File descriptor manipulation using dup()

Command History

• Stores recent commands (circular buffer)
• Execute last command (!!)
• Execute specific command (!n)

Technologies

• C
• Linux system calls
• fork / exec / waitpid
• signals (kill, SIGINT, SIGTSTP, SIGCONT)
• pipes and file descriptors
• memory management

How to Run

1. Compile the project:

   make myshell

2. Run the shell:

   ./myshell

3. Example commands:

   ls -l
   sleep 5 &
   ls | wc -l
   cd ..
   procs

What I Learned

• How command-line interpreters (shells) work internally
• How processes are created and managed using fork/exec
• How to handle signals and control process execution
• How pipes enable inter-process communication
• How to build interactive systems using low-level OS primitives

Contribution

This project was developed independently as part of an Operating Systems course.

I designed, implemented, tested, and debugged all components of the system.