🐚 Simple Shell

A UNIX command line interpreter written in C.

📌 Project Overview

This project is a minimalist implementation of a UNIX shell. It replicates the core behavior of /bin/sh using low-level system calls and without relying on external libraries beyond the standard C library.

The shell supports:

Interactive and non-interactive mode Execution of commands with arguments PATH resolution Built-in commands (exit, env) Proper error handling Correct exit status propagation Memory management (Valgrind clean) 📚 Learning Objectives

Through this project we practiced:

Process creation (fork) Program execution (execve) Process synchronization (wait) Environment handling (environ) PATH parsing Dynamic memory management System call error handling UNIX process lifecycle 🛠 Compilation gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh 🚀 Usage Interactive Mode $ ./hsh $ ls $ ls -l /tmp $ env $ exit Non-Interactive Mode echo "ls -l" | ./hsh ⚙️ Features Implemented (Holberton Requirements) ✅ 1. Basic Shell Displays a prompt in interactive mode Reads user input using getline Executes commands using fork and execve Handles EOF (Ctrl + D) ✅ 2. Handle Arguments

Supports commands with arguments:

ls -l /var

Tokenization is implemented using strtok.

✅ 3. Handle PATH

If the command does not contain / or ., the shell searches for it in the PATH environment variable.

Example:

ls

Internally searches:

/bin/ls /usr/bin/ls ...

If not found → prints error without calling fork.

✅ 4. fork Must Not Be Called If Command Doesn't Exist

The shell validates command existence before forking:

if (cmd_path == NULL) { fprintf(stderr, "./hsh: %d: %s: not found\n", line_num, argv[0]); return (127); }

This satisfies Holberton’s strict requirement.

✅ 5. Built-in: exit

Usage:

exit Exits the shell Returns the last command exit status No arguments required (per project specification) ✅ 6. Built-in: env

Usage:

env

Prints all environment variables using:

extern char **environ; 🧠 Execution Flow START ↓ Display prompt (if interactive) ↓ Read input (getline) ↓ Remove newline ↓ Tokenize input ↓ Check built-ins (exit / env) ↓ Search in PATH (if needed) ↓ If command not found → print error (NO fork) ↓ fork() ↓ Child → execve() Parent → wait() ↓ Return exit status ↓ Repeat 📂 Main Components 🔹 main() Shell loop Input parsing Built-in handling Status tracking 🔹 execute_command() Validates executable path Forks process Calls execve Waits for child Returns exit status 🔹 find_in_path() Parses PATH Iterates directories Constructs full path Validates using stat Returns full path or NULL 🔹 print_env() Iterates through environ Prints environment variables ❌ Error Handling

Handles:

Command not found Fork failure Execve failure Empty input EOF Memory allocation errors

Error format:

./hsh: line_number: command: not found

Exit status 127 is returned when command is not found.

🧵 Memory Management All dynamically allocated memory is freed cmd_path freed after use line freed before exit No memory leaks (Valgrind clean) 🧪 Example Valid Command $ ls main.c hsh README.md Invalid Command $ fakecmd ./hsh: 3: fakecmd: not found 🔐 System Calls Used fork execve wait write access stat getline malloc free 🧾 Return Status Behavior Returns the exit status of the last executed command. Returns 127 if command not found. Built-in exit returns last status. 🧩 Project Constraints (Respected)

✔ No use of system() ✔ No advanced shell features (pipes, redirections, etc.) ✔ No unnecessary forks ✔ Proper PATH handling ✔ No memory leaks ✔ Only allowed functions used

👨‍💻 Authors AZZAM AL DUYULI && ABDULMALIK BIN AQEEL