https://github.com/izzytoot/minishell

This project is about creating a simple shell.
https://github.com/izzytoot/minishell

bash fd processes

Last synced: 3 days ago
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This project is about creating a simple shell.

• Host: GitHub
• URL: https://github.com/izzytoot/minishell
• Owner: izzytoot
• Created: 2025-02-25T16:07:25.000Z (about 1 year ago)
• Default Branch: main
• Last Pushed: 2025-07-03T12:00:25.000Z (10 months ago)
• Last Synced: 2025-12-26T02:29:38.339Z (4 months ago)
• Topics: bash, fd, processes
• Language: C
• Homepage:
• Size: 9.55 MB
• Stars: 1
• Watchers: 1
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

          
# 🐚 MINISHELL 

## ℹ️ About the project

This project was done in partnership with [**Daniela Padilha**](https://github.com/Daniela-Padilha).

It's a polished, mini‑version of a Unix shell written in pure C. This isn’t just an exercise - it’s about building a real, working Command-Line Interface interpreter that plays nicely with pipes, redirections, heredocs, expansions, signals, and error handling.

## 💪 What It Does

1. Reads user input (with readline support for line editing and history);

2. Validates syntax (no unclosed quotes, misplaced operators, etc.);

3. Tokenizes the input and attributed different categories: pipes, redirections, commands (builtins or environment), arguments;

4. Builds an AST (Binary Tree) reflecting pipes, redirections, and commands;

5. Executes it, handling builtins, environment lookup, subprocesses;

The program manages heredocs, multi‑stage redirections, pipes, signals, and exit statuses.

⚠️ We took each piece step by step, ending with a code that works and handles everything gracefully.

## 🧠 Implementation Phases

Here's how it all comes together:

#### a. Syntax Check

- It scans the raw input for basic syntax sanity;

- It detects unclosed quotes, misplaced pipes/redirections, usage of unsuppported operators (&& and ||);

- It refuses to parse broken commands early, printing errors like bash would;

#### b. Tokenization & Sub‑tokenization

- It keeps track of quoting modes to prevent unintended word-splitting;

- It splits input into tokens: words, pipes, redirections;

- It further splits word tokens into filenames, type of command (builtin or environment) or arguments;

- It checks for repeated command words and empty quote situations;

#### c. Binary Tree (AST) Building

- It parses the token stream into a binary tree:

- Pipes (|) create left and right branches;

- Redirections link to command nodes and filename nodes;

- Command nodes will be the last node of the tree.

- This structure reflects evaluation order and establishes an execution flow.

🌳 **BINARY TREE EXAMPLE** 

Input line: cat file.txt | grep hello > out.txt

              PIPE

              "|"

             /    \

         CMD       REDIR_OUT

        "cat"         ">"

         ARG         /   \

       file.txt    CMD   FILENAME

                 "grep"  "out.txt"

                  ARG

                "hello"

Executes left branch first (cat file.txt) and writes into pipe, and right branch after (grep hello > out.txt), reading from pipe.

#### d. Tree Execution

Traverses and executes the AST:

##### d.1 Expansions

- It handles "$VAR", "$?", "$0" and "$EMPTY" expansions;

- It performs word-splitting or joining after expansions unless inside single quotes;

- It replaces the node-argument array;

##### d.2 Heredoc Execution

- It detects how many heredocs are there in the input line;

- It performs the existant heredocs by:

  - detecting the EOF,

  - creating a temporary file,

  - opening a heredoc buffer in a child process,

  - expanding variables inside heredoc if EOF not quoted.

##### d.3 Pipe Execution

- It chains tree nodes through pipes;

- It uses fork(), pipe(), and dup2() to connect child processes;

##### d.4 Redirections Execution

- It applies <, >, and >> to redirect stdin/stdout;

- It opens files with correct flags and uses dup2() to hook them;

- It handles FD opening, duplicating and closing;

- It performs the command linked to the redirect token te correct stdin/stdout;

##### d.5 Command Execution

-  Builtin Commands

  - cd, echo, pwd, export, unset, env, exit;

  - Executed in parent process;

  - It outputs errors and updates exit status without forking.

- Environment Commands

  - Launch external executables using execve()

  - Executed in child process, it searches PATH, handles ENOENT and prints meaningful error messages like bash.

#### e. Transversal Mechanics

These mechanics touch every part of the shell:

Signal Handling

- SIGINT (Ctrl+C): interrupts input or current command, then resets prompt;

- SIGQUIT (Ctrl+\): ignored, same behavior as bash;

- Interactive handling during heredoc, builtins, execution phases.

Exit Code Handling

- Every command sets the correct exit code;

- Exit codes can be checked by expanding $?;

- Child processes inherit parent’s signal-derived or exec-derived exit status;

## 🔥 Build, run and test

```

git clone 

cd minishell

make

./minishell

```

Feel free to test our Minishell. Here is our own list of tests which we compiled troughout this loooooong journey. Have fun!

## 😱 **[OUR LIST OF 282 TESTS](https://www.notion.so/meeru/1d02544e44e2807d9013fd3eefbfebf4?v=1d02544e44e28087a970000c7fb78979)** 😱