CASE STUDY // SYSTEMSSource Code

Minishell

UNIX Command Line Interpreter in C

A custom UNIX shell developed in pure C as part of the 42 Network curriculum. It recreates core bash functionalities including command execution path resolving, pipelines, input/output redirections, environment variable expansions, and signal handling.

LIVE ARCHITECTURE SIMULATORInteractive Demo

Minishell AST & Pipeline Simulator

Interactive trace of lexical analysis, AST parsing, and POSIX process branching.

Lexical Analysis

1. Lexer & Tokenizer

String splitting & quote handling

Input String:

"cat input.txt | grep 'ERROR' > error.log"

Generated Tokens:

catinput.txt|grep'ERROR'>error.log

Accessible Pipeline Breakdown (Screen Reader Data)

Command "cat input.txt | grep 'ERROR' > error.log" parses into 3 pipeline stages: First, tokenization splits string parameters. Next, AST node hierarchy prioritizes redirection operators. Finally, process branching executes cat and grep in parallel via pipe() file descriptors.

Initializing Minishell Pipeline Simulator...

Lines of C

4,500+

Memory Leaks

0 bytes

Norminette

100% Compliant

The Challenge

Handling complex nested tokens, quotes, syntax edge cases, and preventing memory leaks or zombie processes when managing concurrent piped commands.

Architectural Approach

Built a custom Lexer and Abstract Syntax Tree (AST) parser, managed process branching via fork() & execve(), implemented a dual pipeline runner using pipe() and dup2(), and engineered signal handlers for SIGINT/SIGQUIT.

Engineering Impact

Demonstrates low-level UNIX process management, file descriptor manipulation, strict dynamic memory control, and defensive programming in C.

Technical Key Highlights

▸Custom AST Parser for complex quote rules & variable expansion
▸Process management with fork(), execve(), waitpid() & signal traps
▸Robust error reporting matching GNU Bash standards
▸Zero memory leaks verified under Valgrind

Architectural Subsystems

Layer 01Lexer -> Tokenizer -> AST Construction

Layer 02Environment Map (Key-Value linked list)

Layer 03Pipe Executor Matrix (stdin/stdout redirections)

Layer 04Signal Dispatcher (Interactive vs Child mode)

Technologies Used:CUNIX APIPipes & SignalsAST ParserValgrindMakefile