42sh

A POSIX-compliant shell written in C99 from scratch. Implements lexing, parsing, AST construction and execution - no use of system() or popen().

What it does

• Reads shell input interactively or from a script file
• Tokenizes input into a stream of shell tokens
• Parses tokens into an Abstract Syntax Tree using an LL(1) parser
• Executes the AST: commands, pipelines, redirections, control flow
• Expands variables, handles command substitution
• Manages shell environment and builtins

Supported features

• Commands, pipelines (|), sequences (;, &&, ||)
• Redirections (<, >, >>, <<, >&)
• Control flow: if/then/else/fi, while, for, case
• Variable expansion, command substitution ($(...))
• Builtins: cd, echo, exit, export, unset, alias, break, continue, .

Architecture

src/
|-- lexer/              # Tokenization
|   |-- lexer.c         # Token recognition and production
|   |-- lexer_utils.c   # Character classification helpers
|   `-- input_stack.c   # Input source management
|-- parser/             # LL(1) parser -> AST
|   |-- parser_firsts/  # FIRST sets for each grammar rule
|   |-- parser_follows/ # FOLLOW sets for each grammar rule
|   `-- parser_fnct/    # Grammar rule implementations
|-- ast/                # AST node definitions and utilities
|-- execution/          # AST evaluation
|   |-- execution.c     # Node dispatch
|   |-- execute_command/ # Fork + exec
|   `-- builtins/       # Built-in commands
|-- expansion/          # Variable and command substitution
|-- environment/        # Shell variables and environment
|-- hash_map/           # Hash map for variables and aliases
`-- io_backend/         # Input handling (interactive / file)

Build

Requires autotools (autoconf, automake).

autoreconf -i
./configure
make
./42sh

Tests

make check

Team

Baptiste Mathieu - Yann Fernandez Puig - Yann Sarthou - Lenny Taurines

EPITA - Systems programming (ING1)