A Bull Terrier Mini and a Mini Shell too

A minimal POSIX‑like shell implemented in C as part of 42’s Minishell project. It supports a practical subset of bash(1) semantics, robust process management, and precise file descriptor and signal handling. The project includes both the mandatory requirements and the official bonus for logical operators with precedence.

Highlights

• Mandatory: prompt + history (readline), path resolution, redirections (<, >, >>, <<), pipelines (|), environment expansion $VAR, special $?, quotes (', "), and interactive signals (^C, ^D, ^\).
• Bonus: logical operators &&, || with parentheses for precedence.
• Builtins: echo -n, cd, pwd, export, unset, env, exit.

Features

Parsing & expansion

• Lexer with token classification (words, quoted words, operators, redirections, parentheses).
• Quote rules: single quotes do not expand; double quotes do expand $.
• Parameter expansion: $[A-Za-z_][A-Za-z0-9_]* and $?.
• Word splitting occurs after expansions in unquoted parameters, using spaces as separators (simplified Bash behavior).

AST & execution

• Binary AST for operators: PIPE, AND_IF, OR_IF, with nodes for CMD and subshell nodes for (...) (bonus for precedence).
• Redirections attached to command nodes and applied immediately before execve.
• Pipelines use pipe() and dup2() to chain stdin/stdout, maintaining strict file descriptor hygiene.
• wait semantics: the shell reports the last command status in a pipeline; logical operators depend on child statuses.

Builtins

• echo [-n] — handles -n accurately.
• cd [--] [dir] — HOME fallback; errors on too many args; updates PWD/OLDPWD.
• pwd — prints the current working directory using getcwd().
• export [KEY[=VALUE] ...] — validates identifiers; without arguments prints variables in alphabetical order.
• unset [KEY ...] — removes keys.
• env — prints environment variables without options.
• exit [n] — numeric parsing, too many arguments handling, -- as end‑of‑options.

Redirections

• <, >, >> — open/dup2/close handled with error checking.
• << (heredoc) — reads until delimiter (history not updated). Signals handled gracefully during heredoc input.

Signals (interactive UX)

• Parent (shell): SIGINT prints a fresh prompt; SIGQUIT ignored.
• Children: SIGINT/SIGQUIT restored to default for standard command behavior (e.g., cat stopped by ^C, Quit (core dumped) on ^\). On signal termination, $? = 128 + signal.

Example

What’s intentionally out of scope

• Expansion of undefined variables does not create or declare new environment entries; variables can only be created explicitly with export.
• Advanced parameter expansion: ${...}, ${var@Q}, ${#var}, etc.
• Command substitution: $(...) / backticks.
• Arithmetic expansion: $(( ... )).
• Bash‑specific quoting: $'...', $"..." (gettext/ANSI‑C).
• Job control (fg, bg, jobs).
• Globbing beyond the required scope (wildcards handled for current dir only when bonus enabled).

Build & run

Requirements

• Compiler: clang with -Wall -Wextra -Werror.
• GNU Readline development headers.
• Make (provided Makefile targets: all, clean, fclean, re, dev, debug).

The project adheres to the allowed‑functions constraint from the subject (readline, fork/exec, dup/pipe, etc.).

Linux (Debian/Ubuntu)

Prerequisites

sudo apt-get update && sudo apt-get install -y build-essential libreadline-dev

Build & run

make # or make debug, make dev
./miniyeska

Why this project matters

• Processes & pipelines: fork/exec, pipe, dup2, wait/waitpid.
• Descriptors: lifetime, error‑safe closing, redirection discipline.
• Signals: per‑process actions and terminal group management.
• Parsing: correct tokenization, AST, and operator precedence.
• Error handling and exceptional memory cleanup.

Authored by angelurano and g01100001