Minishell - Shell Simulation

Minishell is a project that involves creating a simple shell-like program. It will deepen your understanding of how shells work, including managing user input, executing commands, handling processes, and working with environment variables.

Status

Exemple

Objectives

The goal of this project is to create a shell program that can read user commands, parse them, execute the appropriate system calls, and manage processes, all while providing features like environment variable handling, input/output redirection, and command piping.

Great Resources

GNU Bash Manual

Shell Syntax

Basic shell by Oceano

Mandatory

Program name	minishell
Turn in files	All necessary files to compile the program
Makefile	Yes
External functions	malloc, free, write, read, execve, fork, waitpid, dup, dup2, pipe, signal, exit, getenv, setenv, unsetenv
Libft authorized	No
Description	Simulate a Unix shell environment with process management and command execution.

• The project must be written in C.
• Code must adhere to the Norm.
• No memory leaks are tolerated; all allocated memory must be freed.
• Provide a Makefile to compile the program with flags -Wall -Wextra -Werror.
• The Makefile must include rules for all, clean, fclean, and re.

Functionality

The shell must:

• Parse and execute commands typed by the user.
• Handle simple commands (e.g., ls, pwd, echo).
• Support input and output redirection (<, >, >>).
• Handle piping between commands (|).
• Allow the use of environment variables (e.g., echo $HOME).
• Manage the current working directory using cd.
• Handle both foreground and background processes.

Basic Features

• Command Execution: Use execve to execute commands with arguments.
• Environment Variables: Implement getenv, setenv, and unsetenv for managing environment variables.
• Redirection: Implement input (<), output (>), and append (>>) redirection.
• Piping: Implement the | operator to pipe the output of one command into the input of another.
• Job Control: Handle background processes using the & operator.

Example Usage

$ ./minishell
minishell$ echo "Hello, World!"
Hello, World!
minishell$ ls -l
total 0
-rwxrwxrwx 1 user user 0 Jan 1 12:00 test_file
minishell$ cat < test_file
minishell$ echo "This is a test" > newfile
minishell$ cat newfile
This is a test
minishell$ exit

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Edge Cases to Handle

• Empty Input: Handle empty lines gracefully.
• Invalid Commands: Show an error message when a command is not found.
• Multiple Piping: Handle chains of commands connected with multiple pipes.
• Variable Expansion: Properly expand environment variables like $HOME or $PATH.

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Bonuses

If the mandatory part is completed perfectly, consider the following bonus features:

• Signals Handling: Properly handle signals like SIGINT (Ctrl+C) and SIGQUIT (Ctrl+).
• Advanced Job Control: Implement background processes with & and support for fg, bg, and jobs commands.
• Wildcard Expansion: Support wildcard characters like * and ? in command arguments (e.g., ls *.txt).
• History Management: Implement a history feature that remembers previous commands and allows navigating through them.

Bonus files should be named with the _bonus suffix.

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Key Concepts to Master

• Forking and Executing Processes: Using fork to create child processes and execve to execute programs.
• File Descriptors: Handling redirection and piping using dup and dup2.
• Environment Management: Managing environment variables with getenv, setenv, and unsetenv.
• Signal Handling: Managing and catching signals like SIGINT or SIGQUIT.
• Job Control: Implementing background processes and handling process termination.

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Example Output

$ ./minishell
minishell$ echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin
minishell$ ls | grep shell
minishell$ cat > output.txt
This is a new file
minishell$ cat output.txt
This is a new file
minishell$ exit

This log represents the correct behavior of the shell, where commands are parsed and executed, output is displayed, and files are created or modified.

Disclamer

• 🇬🇧 This project has an educational purpose and you should under no circumstances copy and paste. Cheat is bad. Dont cheat

• 🇫🇷 Ce projet a un but educatif et vous ne devez en auccun cas faire du copier coller. Tricher c'est mal. Ne trichez pas

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©42Perpignan(bepoisso)