🐚 Minishell - A simple Unix Shell

minishell is a core project of the 42 curriculum, designed to implement a simplified Unix shell from scratch. This project involves a deep dive into process management, system calls, signal handling, and complex string parsing.

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📝 Project Description

minishell is a lightweight simulation of Bash. It reads user commands, handles quotes and environment variable expansions, combines programs using pipes and redirections, and reacts to system signals (such as Ctrl-C, Ctrl-D, Ctrl-\) just like a real Bash environment.

The project demands high-quality code, strict memory management (zero leaks allowed), and a profound understanding of Unix internals like Inter-Process Communication (IPC) and File Descriptors.

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✨ Core Features

• Interactive Command Handling: Support for command history using the readline library.
• Process Management: Execution of external binaries via fork and execve using the PATH.
• Redirections:
  • Input redirection <
  • Output redirection >
  • Append mode redirection >>
  • Heredoc << with support for delimiters and signal interruption.
• Pipes: Multi-stage piping | to pass data flow between commands.
• Parsing Logic:
  • Single quotes ' ' (literal interpretation).
  • Double quotes " " (supports variable expansion).
  • Environment variable expansion (e.g., $USER, $HOME, $?).
• Signal Handling: Accurate simulation of Bash's behavior in interactive mode.

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🛠 Built-in Commands

The following standard Bash built-ins are implemented:

• echo (with -n option)
• cd (supports relative and absolute paths)
• pwd
• export (manages environment variables)
• unset
• env
• exit

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🚀 Quick Start

Installation

Clone the repository:

git clone https://github.com/Fiona-87327/42Core_minishell.git
cd 42Core_minishell

Compilation

Use the provided Makefile to compile:

make        # Compiles the 'minishell' executable
make clean  # Removes object files
make fclean # Removes object files and the executable
make re     # Recompiles from scratch

Execution

./minishell

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💡 Usage Examples

1. Basic Pipes and Redirection

minishell> ls -l | grep "m" > result.txt
minishell> cat < result.txt

2. Environment Variable Expansion

minishell> echo "Hello $USER, status of last command: $?"

3. Multi-Piping

minishell> cat Makefile | grep "CC" | wc -l

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🏗 Technical Architecture

Parsing Pipeline

The shell processes input through a multi-stage pipeline:

1. Lexer: Tokenizes the raw input string into meaningful units.
2. Syntax Checker: Validates the sequence of tokens (e.g., preventing | |).
3. Parser: Builds a command structure and resolves environment variables.
4. Executor:
   • Runs built-ins in the parent process if no pipes are present.
   • Forks child processes for external commands and pipelines.
   • Manages dup2 for file descriptor redirections.

Signal Strategy

• Uses a single global variable to track signals as per 42 constraints.
• Ctrl-C: Displays a new prompt on a new line.
• Ctrl-D: Quits the shell (EOF).
• **Ctrl-**: Does nothing in interactive mode to match Bash behavior.

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📚 Resources

• GNU Bash Manual
• The Bash Parser Wiki
• Unix Processes in C - Tutorials

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👥 Authors

• jiyanwang
• mhnatovs

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