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Minishell — As Beautiful as a Shell

🎯 Project Overview

Minishell is a system programming project that consists of building a simple Unix shell from scratch.

The goal is to recreate the core behavior of a standard shell such as bash, including command execution, environment variable handling, pipes, and redirections.

Through this project, you gain practical experience with:

• process management
• file descriptor manipulation
• command parsing
• Unix signals
• system calls

By implementing a shell yourself, you gain a deeper understanding of how operating systems execute programs and manage processes.

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💻 What is a Shell?

A shell is a command-line interpreter that allows users to interact with the operating system by entering commands.

Instead of interacting directly with the kernel, users type commands into the shell, which then:

1. Parses the command
2. Locates the corresponding executable
3. Creates a process
4. Executes the program
5. Returns the result to the user

Shells such as bash, zsh, and sh are essential tools in Unix-based systems and are widely used for system administration, development, and automation.

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⚙️ Technical Specifications

Program Requirements

Component	Specification
Program Name	minishell
Language	C
Compilation	cc -Wall -Wextra -Werror
Authorized Library	libft
External Functions	readline, fork, execve, pipe, dup2, waitpid, etc.

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Key Constraints

• ✅ Only one global variable allowed (used for signal handling)
• ✅ No memory leaks (except those caused internally by readline)
• ✅ Code must follow the 42 Norm
• ✅ The program must not crash under normal usage
• ❌ No interpretation of unclosed quotes
• ❌ Only features required by the subject are implemented

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🔧 Core Features

Basic Shell Behavior

• Display a prompt when waiting for user input

• Maintain a command history

• Execute binaries using:

  • absolute paths
  • relative paths
  • executables found via $PATH

• Proper signal handling

  • Ctrl + C — interrupt command
  • Ctrl + D — exit shell
  • Ctrl + \ — ignored

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🧾 Quote Handling

The shell must correctly interpret quotes:

Quote Type	Behavior
'single quotes'	Prevent interpretation of all special characters
"double quotes"	Allow $ expansion but prevent other interpretations

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🔁 Redirections

The shell supports the following redirection operators:

Operator	Description
<	Redirect input from a file
>	Redirect output to a file
>>	Append output to a file
<<	Here-document (read input until a delimiter)

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🔗 Pipes & Variables

Pipes

Pipes (|) allow chaining commands by redirecting the output of one command to the input of another.

Example:

ls -l | grep minishell

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Environment Variables

The shell must expand environment variables using $.

Examples:

echo $HOME
echo $PATH

Special variable:

$?

Expands to the exit status of the last executed command.

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🛠 Built-in Commands

The shell implements the following built-in commands:

• echo (with -n)
• cd (with relative or absolute paths)
• pwd
• export
• unset
• env
• exit

These commands are executed directly by the shell, without calling external programs.

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🛠 Technical Implementation

Process Management

• Command execution using fork()

• Program execution using execve()

• Process synchronization using:

  • wait()
  • waitpid()

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File Descriptor Management

• Redirections handled using dup() and dup2()

• Pipes implemented using pipe()

• File handling using:

  • open()
  • close()
  • read()
  • write()

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Input & Memory Management

• Readline library used for command input and history

• Dynamic memory allocation using:

  • malloc
  • free

• Environment variable handling through getenv

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🎯 Learning Objectives

This project focuses on core concepts in Unix system programming:

• Process creation and control
• File descriptor manipulation
• Signal handling
• Command parsing and tokenization
• Memory management
• Low-level operating system interaction

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📚 Additional Information

More implementation details and documentation can be found in the Infor folder.