Unix Shell

Overview

This project implements a simple Unix shell in C that supports built-in commands, command execution with forking, input/output redirection, and pipes. The shell reads user input, parses commands, and executes them accordingly.

Features

• Built-in commands:
  • help - Displays available commands.
  • exit - Exits the shell.
  • cd <dir> - Changes the current directory.
  • mkdir <dir> - Creates a new directory.
  • !! - Repeats the last executed command.
• Command Execution:
  • Runs standard Unix commands using execvp().
  • Supports single commands and multiple arguments.
• Input/Output Redirection:
  • Uses > to redirect output to a file.
  • Uses < to read input from a file.
• Piping Support:
  • Recognizes the | operator to pass output between commands.
• Special Commands:
  • ECHO - Prints commands without redirection or pipes.
  • IO - Prints filenames used for input/output redirection.
  • PIPE - Displays pipeline execution steps.

Installation & Compilation

To compile the shell, run:

gcc -o shell shell.c

To start the shell, run:

./shell

Usage Examples

Running Basic Commands

$ ls
$ whoami
$ date

Using Built-in Commands

$ help
$ mkdir test_folder
$ cd test_folder
$ !!

Input & Output Redirection

$ echo "Hello" > output.txt
$ cat < output.txt

Pipes

$ ls | wc -l

Special Features

$ cal feb 2025 > t.txt ECHO  # Output: "cal feb 2025"
$ cat < input.txt IO  # Output: "LT input.txt"
$ cat shell.c | wc PIPE  # Output: "PIPE wc"

Known Issues

• The shell does not yet support complex piping with multiple redirections.
• Background process execution (&) is not implemented.

Future Improvements

• Implement signal handling (Ctrl+C to terminate processes cleanly).
• Add support for background processes.
• Improve error handling for invalid commands.

Author

• Developed as part of a Unix shell programming assignment.