🇫🇷 Version française disponible ici

---

Project presentation - minishell

Description

This project consists of creating a miniature Unix shell in C.

The goal is to implement a fully functional command-line interpreter that executes commands, handles built-ins, pipes, redirections, environment variables, and signals. It mimics the behavior of a real shell while emphasizing memory management, process handling, and input parsing.

This project involves:

• Parsing user input and tokenizing commands
• Handling child processes and inter-process communication
• Managing signals (Ctrl-C, Ctrl-D, Ctrl-\)
• Implementing input/output redirections (<, >, >>, <<)
• Supporting pipes (|)
• Expanding environment variables ($VAR) and $? (last exit status)
• Implementing mandatory built-in commands
• Displaying a prompt and maintaining a working command history

---

Languages & Technologies

Language

• C (C99 standard)

Technologies

• Makefile
• Unix system calls (fork, execve, pipe, dup2, waitpid)
• I/O redirection
• Signal handling (SIGINT, SIGQUIT)
• Environment variable management
• Linked lists (for managing commands and tokens)
• Dynamic memory management
• String parsing and manipulation

---

Shell Features

Prompt & Command Input

• The shell displays a prompt when waiting for a new command.
• Commands are read from standard input.
• History is maintained during the session.

Built-in commands

Command	Description
echo	Prints text to the terminal; supports -n option
cd	Changes the current directory (relative or absolute path)
pwd	Prints the current working directory
export	Sets environment variables
unset	Removes environment variables
env	Displays environment variables
exit	Exits the shell

Command execution

The program :

• executes external commands using execve
• searches executables either via $PATH or using relative/absolute paths
• handles only one global variable to store received signals (SIGINT, SIGQUIT); the handler does not access the main data structures

Redirections

• < redirects input
• > redirects output (overwrite)
• >> redirects output (append)
• << (here-doc) : reads input until a line containing the delimiter is seen. History is not updated for here-doc input.

Pipes

• Commands can be chained using | : each command’s output is connected to the next command’s input via a pipe

Quotes & Special characters

• Single quotes '...' prevent interpretation of meta-characters
• Double quotes "..." prevent interpretation of meta-characters except $ for environment variable expansion
• Other meta-characters such as \ and ; are not interpreted
• Wildcards (*) are not supported

Environment variables

• $VAR expands to the variable’s value.
• $? expands to the exit status of the most recently executed foreground pipeline.

Signal handling

• Ctrl-C displays a new prompt on a new line.
• Ctrl-D exits the shell.
• Ctrl-\ does nothing in interactive mode.

---

Notes

Understanding and implementing pipex is extremely useful for minishell, as it introduces core concepts such as pipes, process creation, and I/O redirection. These mechanisms are fundamental to minishell for executing pipelines (cmd1 | cmd2) and managing input/output redirections. Completing pipex first provides a strong foundation for building minishell.

---

Using minishell

Makefile rules

1. all as default rule: builds the project, compiles all .c files into .o, then creates the program (minishell)
2. clean : removes compiled object files (.o)
3. fclean : clean rule and removes the executable (minishell)
4. re : fclean then all rule

---

How to use minishell

Note : the minishell project works on its own and uses the libft library. Since the library is added as a submodule, you need to clone the repository with it.

1. Clone minishell in a folder first : git clone --recurse-submodules https://github.com/bibickette/minishell.git
2. Go to the minishell folder then compile it : cd minishell && make
3. Run ./minishell without any argument
4. You can now type any commands like in a normal shell : echo "hello world ! " | cat -e

Valgrind & memory checks

minishell was tested using Valgrind to ensure there are no memory leaks and that all allocated memory is properly freed. Like the pipex project, it relies on system calls such as fork, execve, pipe... some memory may still appear as reachable due to system-level allocations performed by the system and libraries. To obtain clean and meaningful results, a suppression file is used.

You can run minishell with Valgrind using the following command : valgrind --leak-check=full --show-leak-kinds=all --track-fds=yes --suppressions=all.supp ./minishell

The all.supp file filters out known and unavoidable leaks, this allows Valgrind to focus only on real memory leaks caused by the project itself.

You can now test my minishell !

---

Project validation date : October 2, 2024