pipex

A 42 School project reimplementing how a shell pipe (cmd1 | cmd2) works, using the fork, pipe, dup2, and execve system calls. The goal is to get a deep, hands-on understanding of redirections and inter-process communication on Unix.

Table of Contents

• Overview
• Build
• Usage
• Bonus
• Project Structure
• Technical Details

Overview

pipex reproduces the shell command:

< infile cmd1 | cmd2 > outfile

without going through /bin/sh. Each command runs in its own child process, with children connected to each other via pipe() and wired to the right input/output through dup2(). The program resolves each command's executable path itself by searching the directories listed in the PATH environment variable.

Build

make        # builds the pipex executable (mandatory part)
make bonus  # builds the pipex executable (bonus part)
make clean  # removes object files
make fclean # removes object files + the executable
make re     # fclean then all

Usage

Mandatory version:

./pipex infile cmd1 cmd2 outfile
# equivalent to: < infile cmd1 | cmd2 > outfile

Example:

./pipex infile "grep foo" "wc -l" outfile

Bonus

The bonus version supports:

• An unlimited number of commands, chained into a single pipeline:

  ./pipex infile cmd1 cmd2 cmd3 ... cmdN outfile

• here_doc, which replaces the input file with standard input delimited by a terminator (like << in shell):

  ./pipex here_doc LIMITER cmd1 cmd2 ... cmdN outfile

• Writing to outfile happens in append mode when here_doc is used, mirroring >>.

Project Structure

.
├── includes/
│   ├── pipex.h          # structs, prototypes, internal libft
│   └── pipex_bonus.h    # bonus-specific prototypes
├── srcs/
│   ├── pipex.c          # main (mandatory part)
│   ├── pipex_bonus.c    # main (bonus part) + here_doc handling
│   ├── pipeline.c       # fork/pipe orchestration for each command
│   ├── execute.c        # dup2, command lookup and execution (execve)
│   ├── path.c           # PATH resolution to locate the executable
│   ├── fd_utils.c       # safe opening/closing of files and file descriptors
│   ├── ft_split.c       # string splitting (libft)
│   ├── str_utils.c      # string utilities (libft)
│   └── utils.c          # fatal error handling
└── Makefile

Technical Details

• Command lookup: if the command contains a /, it is used as-is; otherwise, each directory in $PATH is tested until a matching executable is found (path.c).
• Exit codes: the program returns the exit status of the last command in the pipeline (126 if found but not executable, 127 if not found), matching standard shell behavior.
• Generic pipeline: the number of commands is not fixed — pipeline.c dynamically creates one pipe and one fork per stage, closing every unused file descriptor in each process to avoid descriptor leaks or read blocking.
• Error handling: allocations, fork, pipe, and file opens are all checked; any fatal error frees already-allocated resources before exiting cleanly.

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Note: project completed as part of the 42 curriculum, solo, scored 125/100.