🔗 Pipex - 42 School Project

Welcome to Pipex! 🎉 This is a project from Rank 2 at 42 School that introduces us to the world of pipes, processes, and inter-process communication in Unix systems. The goal is to recreate the behavior of shell pipes using system calls like pipe(), fork(), dup2(), and execve().

This project simulates the shell command: < file1 cmd1 | cmd2 > file2 🚀

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📂 Project Structure

pipex/ ├── include/pipex.h # Header file (.h)
├── src/ # Source files (.c)
│ ├── main.c # Main program logic
│ ├── processes.c # Process management
│ ├── execution.c # Command execution
│ └── errorhandler.c # Error handling
├── obj/ # Object files directory
├── libft/ # Libft library
├── .gitignore
├── Makefile # Makefile to compile the project
└── README.md # This file

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📜 Function Overview

🎯 Main Functions

• main(int argc, char **argv, char **envp): Entry point, validates arguments and orchestrates the pipeline
• child_process(int *pipe, char **argv, char **envp): Handles the first command execution
• parent_process(int *pipe, char **argv, char **envp): Handles the second command execution

🔧 Utility Functions

• execute(char **envp, char *argv): Executes commands using execve()
• error(int code): Handles different types of errors
• free_split(char **split): Frees memory allocated for split arrays

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⚙️ How It Works

🎯 Program Flow

1. Argument Validation: Checks for exactly 4 arguments (input file, cmd1, cmd2, output file)
2. Pipe Creation: Creates a pipe for inter-process communication
3. Process Forking: Creates child and parent processes
4. File Redirection: Redirects input/output using dup2()
5. Command Execution: Executes commands using execve()

🔧 Technical Implementation

• Pipes: Used for communication between processes
• Fork: Creates separate processes for each command
• Dup2: Redirects file descriptors for input/output
• Execve: Replaces process image with command execution
• Wait: Parent process waits for child completion

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🛠️ How to Use

📦 Compilation

To compile the program, run:

make

This will generate the pipex executable.

🧩 Usage

The program takes exactly 4 arguments:

./pipex file1 cmd1 cmd2 file2

Where:

• file1: Input file to read from
• cmd1: First command to execute
• cmd2: Second command to execute
• file2: Output file to write to

💡 Usage Examples

Basic Example

./pipex input.txt "grep hello" "wc -l" output.txt

Equivalent to: < input.txt grep hello | wc -l > output.txt

More Examples

# Count lines containing "error" in a log file
./pipex server.log "grep error" "wc -l" error_count.txt

# Extract and sort unique usernames
./pipex users.txt "cut -d: -f1" "sort -u" sorted_users.txt

# Find and count .c files
./pipex file_list.txt "grep '\.c$'" "wc -l" c_files_count.txt

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🎯 Key Learning Objectives

• Process Management: Understanding how to create and manage processes with fork()
• Inter-Process Communication: Learning to use pipes for data transfer between processes
• File Descriptor Manipulation: Mastering dup2() for input/output redirection
• System Calls: Working with low-level system functions
• Command Execution: Understanding how shells execute commands with execve()
• Error Handling: Proper error management in system programming

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✅ Project Requirements

• ✅ Handle exactly 4 arguments
• ✅ Create a pipe between two commands
• ✅ Execute commands in separate processes
• ✅ Handle input/output file redirection
• ✅ Proper error handling for all edge cases
• ✅ No memory leaks
• ✅ Handle command not found errors
• ✅ Behave exactly like shell pipes

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🔧 System Calls Used

• pipe(): Creates a pipe for inter-process communication
• fork(): Creates a new process
• dup2(): Duplicates file descriptors for redirection
• execve(): Executes a command
• wait(): Waits for child process completion
• open(): Opens files for reading/writing
• close(): Closes file descriptors

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🚨 Error Handling

The program handles various error conditions:

• Invalid arguments: Wrong number of arguments
• File errors: Input file not found, output file creation failed
• Pipe errors: Pipe creation failure
• Fork errors: Process creation failure
• Command errors: Command not found or execution failure
• Permission errors: Insufficient file permissions

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🚀 Advanced Features

Multiple Command Support

While the basic version handles two commands, the implementation can be extended to support multiple commands in a pipeline.

Here_doc Support (Bonus)

The project can be extended to support here_doc functionality:

./pipex here_doc LIMITER cmd1 cmd2 file

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🔍 Testing

Test your pipex with various commands:

# Test basic functionality
./pipex /etc/passwd "grep root" "wc -l" output.txt
< /etc/passwd grep root | wc -l

# Compare outputs - they should be identical

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💡 Tips for Success

1. Understand the pipe mechanism - Data flows from write end to read end
2. Close unnecessary file descriptors - Prevent resource leaks
3. Handle edge cases - Empty files, non-existent commands, etc.
4. Test with real shell commands - Compare behavior with actual pipes
5. Use proper error codes - Different errors should have different codes

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Made with ❤️ at 42 Madrid