MINISHELL

This README provides an overview of the Minishell project for 42 School Hive Helsinki, detailing its objectives and offering guidance. The goal of the project is to implement a simplified shell (command interpreter) in C, following the 42 Norm and POSIX standards. It should handle typical Unix commands, redirections, and pipe operations.

Here is a short demonstration of the Minishell in action:

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Table of Contents

1. Introduction
2. Project Structure
3. Installation and Compilation
4. Running the Program
5. Minishell Features
   • Basic Commands
   • Redirections
   • Pipes
   • Built-in Commands
   • Signal Handling
   • Extra Features
6. Examples
7. Debugging and Error Handling
8. Conclusion

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Introduction

Minishell is a project at Hive Helsinki aiming to enhance your understanding of:

• Process creation and management (fork, exec, wait).
• File descriptors and their redirection.
• Pipes, enabling inter-process communication.
• Signal handling (SIGINT, SIGQUIT, etc.).
• Structural coding and modular design.

The general purpose is to provide a simplified shell that allows users to execute commands, leverage built-in commands, and use many Bash-like functionalities.

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Project Structure

Minishell can be divided into several major components:

1. Parser – Parses the user’s input (commands, arguments, pipes, redirections, etc.).
2. Executor – Executes parsed commands (forks new processes and calls execve).
3. Redirections – Manages <, >, >>, and << (heredoc) redirections.
4. Built-in Commands – Implements certain shell internal commands (e.g., cd, echo, env, exit).
5. Signal Handling – Handles signals such as Ctrl-C, Ctrl-\ in both parent and child processes.
6. Helper Functions – Includes memory management, error printing, file open/read/close utilities, etc.

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Installation and Compilation

Below is a general example of how to build the project.

1. Ensure you have gcc or another C compiler installed, as well as make.
2. Download or clone the project source code.
3. Change directory into the project folder:

   cd minishell

4. Run: make:

   make

   This will compile the necessary .c files and produce an executable (e.g., minishell).

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Running the Program

Once successfully compiled, launch Minishell by running:

./minishell

You should see a prompt minishell%. Try typing the same commands you would in Bash:

minishell% echo "Hello Minishell!"
Hello Minishell!
minishell% cd ..
minishell% ls -l

To exit, use the exit command or press Ctrl-D

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Minishell Features

Basic Commands

• Minishell searches for the command path in the $PATH environment variable, or checks if it is a built-in command.
• If found, Minishell forks a new process and calls execve.
• If the command is not found, an error message is printed.

Redirections

• > Redirects output to the specified file (overwrites the file).
• >> Appends output to the end of the specified file.
• < Reads input from the specified file.
• << (heredoc) Reads input from user input until the specified delimiter is reached, then writes that input into a pipe for the command to read.

Pipes

• | Connects multiple commands on a single command line. The output of one command becomes the input of the next.
• Minishell creates a pipe for each |, adjusting the stdin/stdout in each child process accordingly.

Built-in Commands

• echo Prints the provided arguments.
• cd Changes the current working directory.
• pwd Prints the current working directory path.
• export Sets environment variables.
• unset Removes environment variables.
• env Displays the current environment variables.
• exit Exits Minishell.

Signal Handling

• SIGINT (Ctrl-C): Interrupts the current process or returns Minishell to a new prompt.
• SIGQUIT (Ctrl-): May terminate the currently running process or remain silent, depending on your implementation.
• It is important to distinguish whether you are in the parent or child process to manage signals correctly.

Extra Features

• $? – Variable that stores the exit status of the last executed command.
• Quote parsing – Handling strings in single and double quotes.

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Examples

1. Simple Command

minishell% echo "Hello World"
Hello World

2. Redirection

minishell% ls > filelist.txt
minishell% cat filelist.txt
... (content of the ls command)

3. Pipe

minishell% ls -l | grep minishell
drwxr-xr-x   5 user  user       160 Dec 20 10:44 minishell

4. Heredoc

minishell% cat << EOF
> Some text
> more text
> EOF
Some text
more text

5. Built-in Commands (cd and pwd)

minishell% pwd
/home/user/projects/minishell
minishell% cd ..
minishell% pwd
/home/user/projects

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Debugging and Error Handling

• Debug prints: If you'd like to compile Minishell in debug mode, you can define debug prints in your header files to display additional logs (such as parser states and token details).
• Error messages: It's crucial to detect cases where commands or files are missing, or the user provided incomplete arguments (for example, cd without a path). Make sure you return clear messages (e.g., minishell: command not found: ...).
• Memory leaks: A suppression file (readline.supp) is provided so Valgrind ignores any readline-specific leaks. This lets you focus on managing your Minishell’s resources. Below is an example command for running Valgrind with the suppression file:

  valgrind -v --suppressions=readline.supp --leak-check=full --show-leak-kinds=all ./minishell

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Conclusion

The Minishell project turned out to be much larger and more demanding than I initially anticipated. Working with process management, pipes, and redirections gave me a far deeper understanding of how a command-line interpreter operates under the hood. In particular, the multi-stage parsing logic and signal handling required careful planning and intensive testing.

Although it took a considerable amount of time and effort, it was a highly rewarding learning experience. I now feel more confident handling processes, file descriptors, and structuring. I believe these skills will be valuable for future projects and challenges.