A modern command-line shell implemented from first principles using POSIX APIs. Learn process management (fork(), execvp(), waitpid()), file descriptors, I/O redirection, pipes, environment variables, signals, and job control.
- Interactive shell with prompt and input reading
- Command parsing & tokenization (including quoting, escaping, variables)
- Built-in commands:
cd,pwd,echo,export,unset,exit,help - External command execution via
fork()→execvp()→waitpid() - I/O redirection:
>(truncate),>>(append),<(input) - Pipes (
|) for chaining commands - Environment variable expansion
- Background execution with
& - Process groups via
setpgid() - Signal handling setup
- CMake 3.20+ build system (Debug/Release)
- Compiler warnings enabled (
-Wall,-Wextra,-pedantic) - Sanitizer-ready (AddressSanitizer, UBSanitor)
- Modular architecture with separate source files
- Tested on Linux
- OS: Linux (tested on Kali Linux Rolling)
- Compiler: G++ 15+ / Clang 15+
- CMake: 3.20 or later
# Configure project
cmake -S . -B build
# Build (defaults to Debug)
cmake --build build
# Run the shell
./build/myshellTest without interactive prompt:
printf 'echo hello\nexit\n' | ./build/myshell$ ./build/myshell
myshell$ pwd
/home/user/myshell
myshell$ echo "Hello, $(whoami)!"
Hello, user!
myshell$ date > /tmp/date.txt
myshell$ cat /tmp/date.txt
Mon Sep 16 2026
myshell$ ls | grep -i readme
README.md
myshell$ env | grep -i path
PATH=/usr/local/bin:/usr/bin:...
myshell$ exitmyshell/
├── include/myshell/ # Header files (.hpp)
│ ├── builtins.hpp # Built-in command declarations
│ ├── executor.hpp # Command execution logic
│ ├── parser.hpp # Text parsing
│ ├── shell.hpp # REPL interface
│ ├── types.hpp # Core data structures
│ └── jobs.hpp # Job control (future)
├── src/ # Implementation files
│ ├── builtins.cpp # Built-in command implementations
│ ├── executor.cpp # Execution + redirection + pipes
│ ├── jobs.cpp # Background process management
│ ├── main.cpp # Entry point
│ ├── parser.cpp # Lexer/parser implementation
│ └── shell.cpp # REPL & prompt handling
├── tests/ # Unit/integration tests
│ ├── test_redirections.cpp
│ └── test_shell_smoke.cpp
├── docs/ # Documentation (coming soon)
│ ├── architecture.md → See README instead now
│ └── internals.md → See README instead now
├── .github/workflows/ → CI/CD workflows (coming soon)
├── CMakeLists.txt # Build configuration
├── MILESTONE_PROGRESS.md # Development milestones
└── README.md # This file
After studying this project, you'll understand:
| Concept | Why It Matters |
|---|---|
fork() |
Creates a new process (copy-on-write) |
execvp() |
Replaces current process image with new program |
waitpid() |
Wait for child + retrieve exit status |
| File descriptors (0,1,2) | stdin/stdout/stderr manipulation |
dup2() / open() |
Core redirection implementation |
pipe() |
Inter-process communication |
| Environment inheritance | Children inherit parent's environment |
# Run all tests (if they pass)
cd build && ctest
# Or test manually:
printf 'echo first > /tmp/test.txt\necho second >> /tmp/test.txt\ncat /tmp/test.txt\n' | ../build/myshell- Level 2–5: Built-ins, process execution, redirection, pipes, environment
- Level 6: Full quoting system
- Level 9: Background process management
- Level 13: Comprehensive unit tests
- Advanced variable expansion
- Signal handling for job control (
fg,bg,jobs) - Command substitution
$() - History, readline, tabs completion
- CI/CD on GitHub Actions
Currently (by design):
- No command chaining with
&&/||or; - No glob expansion (
*.txt) - No advanced redirection (
>file 2>&1,<&0) - Basic parser (no heredocs yet)
MIT License — see LICENSE file in repository.
Pull requests welcome! See docs/architecture.md for design decisions.
This is an educational project. Found a bug or have questions? Create an issue!