minishell — Custom Unix Shell

A fully functional Unix shell implementation in C, supporting command execution, pipes, I/O redirections, variable expansion, and built-in commands. Demonstrates core systems programming concepts including process management, signal handling, and file descriptor manipulation.

Features

Core Functionality

• Lexer & Tokenizer: Complete tokenization with quote handling and operator detection
• Recursive Descent Parser: AST generation with full syntax validation
• Command Execution: Process creation, parent/child management via fork/exec
• Pipes: Multi-command pipeline support with proper file descriptor management
• I/O Redirections: Input (<), output (>), append (>>), and heredoc (<<)

Built-in Commands

• echo — Print text (with -n flag support)
• cd — Change directory with OLDPWD tracking
• pwd — Print working directory
• export — Set environment variables
• unset — Remove environment variables
• env — Display environment
• exit — Terminate shell with exit code

Advanced Features

• Variable Expansion: $VAR and $? (exit status)
• Heredoc: Multi-line input with <<DELIMITER
• Signal Handling: SIGINT (Ctrl+C) and SIGQUIT (Ctrl+) management
• Environment Management: Full environment variable support and regeneration
• Quote Handling: Single quotes (literal) and double quotes (with expansion)

Architecture

Input → Tokenizer → Parser → Expander → Syntax Check → Executor
                                                           ↓
                                                      Command Exec
                                                      (fork/exec)

Key modules:

• src/tokenization/ — Lexical analysis
• src/syntax/ — Parser and syntax validation
• src/expansion/ — Variable and special character expansion
• src/execution/ — Command execution and process management
• src/builtins/ — Built-in command implementations
• src/environment/ — Environment variable handling
• src/signals/ — Signal handlers

Build & Run

make              # Compile
./minishell       # Run shell
make clean        # Remove .o files
make fclean       # Remove all build artifacts
make re           # Rebuild

Example Usage

$ ls -la | grep minishell
$ echo "Hello $USER"
$ export MY_VAR=value && echo $MY_VAR
$ cd ~ && pwd
$ cat << EOF
> multiline
> input
> EOF

Technical Highlights

• Memory Management: Comprehensive cleanup routines to prevent leaks
• File Descriptor Handling: Proper management of pipes and redirections
• Process Synchronization: waitpid() for process state tracking
• Signal Safety: Non-blocking signal handlers
• POSIX Compliance: Follows POSIX shell specification where applicable

Limitations & Future Work

• No job control (fg, bg, jobs)
• No history file persistence
• No readline history navigation (uses raw readline library)
• No glob expansion (*, ?)
• No command substitution (`command`)

Requirements

• GCC/Clang compiler
• Linux/Unix environment
• GNU Make
• POSIX-compliant C library

Project Stats

• Lines of Code: ~3,500 (excluding libft)
• Number of Commits: 15+ logical phases
• Build Time: < 1 second
• Memory Leaks: 0 (validated with Valgrind)