Mini Unix Shell

This project implements a simplified Unix shell in C using an incremental development approach.

Instead of implementing the entire shell at once, the system is built through twelve small programs, where each stage introduces one fundamental concept of Unix systems programming such as process creation, command execution, pipes, and file descriptor redirection.

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Features

• Command execution using fork() and exec
• Command parsing with arguments
• Pipes between processes
• Input and output redirection
• Basic interactive shell loop

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Project Structure

mini-unix-shell
│
├── report
│   └── myshell.pdf
│
├── src
│   ├── 1gets.c
│   ├── 2execlp.c
│   ├── 3strtok.c
│   ├── 4strtok.c
│   ├── 5dup.c
│   ├── 6pipe.c
│   ├── 7pipe.c
│   ├── 8pipe.c
│   ├── 9pipe.c
│   ├── 10pipe.c
│   ├── 11pipe.c
│   └── 12shell.c
│
├── README.md
├── LICENSE
└── .gitignore

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Development Stages

Program	Concept
1gets.c	Basic shell loop
2execlp.c	Command execution
3strtok.c / 4strtok.c	Command parsing
5dup.c	File descriptor redirection
6pipe.c	Basic pipes
7pipe.c	Two-process pipeline
8pipe.c	User pipe commands
9pipe.c / 10pipe.c	Flexible command execution
11pipe.c	Output redirection
12shell.c	Final shell implementation

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Example Commands

who | wc -l
ls -l > output.txt
ls -l | sort > sorted_output.txt
sort < input.txt > sorted.txt

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Build

Compile the final shell:

gcc src/12shell.c -o myshell

Run:

./myshell

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Project Report

A detailed explanation of the design and implementation is available in:

report/myshell.pdf

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Author

Nabin Kumar Singh
MS Electrical Engineering
University of Alabama in Huntsville