Minishell

A simple bash-like shell we built from scratch. The idea was to understand how commands actually run under the hood—lexing, parsing, expanding variables, and execution of the actual command.

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The Team

MXCALLL Lexer, Parser & Expansion

moniross Execution & Signals

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How It Works

Input: echo "Hello $USER" | grep $USER > output.txt
  ↓
[Lexer] → tokens: ["echo", "Hello $USER", "|", "grep", "$USER", ">", "output.txt"]
  ↓
[Parser] → commands: [{cmd: echo, args: [...]}, {cmd: grep, args: [...], output: output.txt}]
  ↓
[Expander] → resolve variables, remove quotes
  ↓
[Executor] → fork, pipe, redirect, execute, wait

When you type a command and hit enter, here's what happens:

1. Reading input – We use readline() to grab what you typed and add it to history.

2. Tokenizing – The lexer breaks your input into tokens (words, operators like |, >, <, etc.). Think of it like splitting a sentence into individual words and punctuation marks.

3. Parsing – The parser looks at those tokens and builds command structures. It figures out what's a command, what's an argument, where redirections go, and how pipes connect things.

4. Expanding – Before running anything, we handle stuff like $USER or $? and strip away quotes that bash would remove.

5. Executing – This is where things get real:

   • We open heredocs if needed
   • Set up pipes between commands
   • Fork child processes for external commands
   • Run builtins directly without forking
   • Wait for everything to finish and collect exit codes

6. Cleanup – Close file descriptors, free memory, and get ready for the next command.

The whole loop lives in src/main.c, and each stage has its own folder under src/ (1-Lexer, 2-Parser, 3-Expander, 4-Executer).

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Project Structure

Minishell/
├── src/
│   ├── main.c              # Main loop and signal setup
│   ├── 1-Lexer/           # Tokenization
│   ├── 2-Parser/          # Building command structures
│   ├── 3-Expander/        # Variable expansion & quotes
│   ├── 4-Executer/        # Process execution
│   └── builtins/          # Built-in commands (cd, echo, etc.)
├── includes/
│   └── minishell.h        # Shared headers and structs
└── libft/                 # Helper functions

What We Built

Features of Our Minishell

• Prompt with history
• Quotes handling (' and ")
• Redirections (<, >, <<, >>)
• Pipes (|)
• Environment variables ($VAR, $?)
• Signals (ctrl-C, ctrl-D, ctrl-)
• Builtins: echo -n, cd, pwd, export, unset, env, exit

Things That Are Not Supported

• Logical operators (&&, ||) with parenthesis
• Wildcards (*)