42sh POSIX

The Project

42sh is a major project in the EPITA curriculum. The goal is to develop a POSIX-compliant shell capable of interpreting scripts and handling user interaction, similar to Bash.

Technical Context

While access to the standard C library is allowed, specific helper functions like system, glob, regexec, and wordexp were strictly forbidden. This constraint forced us to manually reimplement complex logic such as pattern matching and command execution flows.

Key technical achievements include robust pipeline orchestration, recursive descent parsing generating an Abstract Syntax Tree (AST), and signal handling.

Features Implemented (Step 4)

We successfully validated the project up to Step 4. The shell supports:

• Parsing & AST: A custom Lexer and Parser capable of handling complex grammar rules.
• Control Structures: Full support for if/else/elif, while, until, for loops, and case statements.
• Execution Engine: Process creation using fork, execve (and execvp), and waitpid.
• Redirections & Pipes: Management of file descriptors for pipelines (|) and redirections (>, <, >>, <<).
• Expansions: Variable expansion ($var, ${var}), return codes ($?), and Process ID ($$).
• Builtins: Implementation of cd, exit, export, unset, continue, break, and source (dot).

Development Environment

The project was built using professional industry tools:

• Language: C (C99 Standard) with strict compiler flags (-Werror -Wall -Wextra -pedantic).
• Build System: GNU Autotools (autoreconf, configure, make).
• Testing: A custom functional test suite to ensure non-regression against Bash POSIX behavior.

Conclusion

This project was an intensive deep dive into software architecture and the Unix philosophy. It required rigor in memory management (detecting leaks with Valgrind) and reliability. Note: The source code is private due to academic integrity rules.