Custom Unix Shell Implementation

A minimal Unix-like shell supporting command execution, piping, redirections, background execution, and command history.

Overview

This project is a custom Unix shell implementation that supports various shell functionalities, including command execution, piping, redirections, background execution, logical operators, and command history.

Features Implemented

Basic Command Execution

• Supports execution of external programs (e.g., ls, pwd, echo, whoami, cd).

Input and Output Redirection

• Output Redirection (>): Redirects command output to a file:

  echo "Hello" > file.txt

• Append Mode (>>): Appends output to a file instead of overwriting:

  echo "Hello again" >> file.txt

• Input Redirection (<): Uses a file as input for a command:

  cat < file.txt

Piping (|)

• Allows connecting multiple commands by passing output from one command as input to another:

  ls | wc -l

Background Execution (&)

• Enables running commands in the background without blocking the shell:

  sleep 5 &

• Displays the process ID (PID) of background processes.

Logical Operators (&& and ||)

• AND (&&): Executes the second command only if the first one succeeds:

  ls && echo "Success"

• OR (||): Executes the second command only if the first one fails:

  ls nonexistent || echo "Failed"

Command History (!n)

• Allows executing previous commands using !n, where n is the command number:

  !1  # Executes the first command in history

Compile and Run

Compile the Shell

gcc sh.c -o utsh

Run the Shell

./utsh

Example Commands

utsh$ ls
utsh$ pwd
utsh$ echo "Hello, Shell!"
utsh$ ls | wc -l
utsh$ echo "Output" > output.txt
utsh$ cat < output.txt
utsh$ sleep 5 &
utsh$ ls && echo "Command successful"
utsh$ ls nonexistent || echo "Command failed"
utsh$ !1  # Executes the first command in history

Notes

• This shell does not support advanced features like job control (fg, bg, kill).
• It assumes valid input formats and does not handle deeply nested piping.

Demo

Watch on YouTube

License

This project is developed as part of CS5460/6460 Operating Systems Assignment.

Credit

Developed by Abhijeet Pachpute 😎