Minishell

Description

Minishell is a lightweight implementation of POSIX shell designed to provide a minimalistic command-line interface for interacting with an operating system.

Minishell will support the following features:

1. Display a user-friendly prompt when waiting for a new command, providing an intuitive user experience.
2. Maintain a working command history, allowing users to easily navigate and recall previously executed commands.
3. Search and launch the correct executable based on PATH variable or relative/absolute paths, offering a smooth command execution process.
4. Forgo support for unclosed quotes and special characters such as \ (backlash) and ; (semicolon), ensuring a cleaner and less error-prone user experience.
5. Support single quotes ' , preventing the shell from interpreting characters within the quoted sequence, allowing users to work with literal strings.
6. Support double quotes " , preventing the shell from interpreting characters within the quoted sequence, except for the $ (dollar sign) for variable expansion.
7. Provide support for I/O redirections and here documents (< , > , >> , << ), enabling users to redirect input and output between commands and files.
8. Handle environment variables, allowing users to set, modify, and retrieve variables as needed.
9. Manage ctrl-C , ctrl-D and ctrl-\ signals, ensuring proper behavior similar to that of bash.
10. Support special variables, such as $?, for context-based command behavior.
11. Support compound commands with a subshell execution () .
12. Support command lists with && (AND_IF) and || (OR_IF) operators.
13. Wildcard * support for current working directory.
14. Implement built-in commands, including echo, cd, pwd, export, unset, env and exit, providing essential shell functionality out-of-the-box.

Installation

If you don't have gcc or GNU make do these commands:

sudo apt update
sudo apt install build-essential

To install readline use this command:

tar -xf readline-8.2.tar
make config

To install minishell just run make in the root of the cloned repository.

Architecture

Minishell's architecture is designed to provide a modular and efficient command-line interface. The project is structured into five distinct modules, each responsible for a specific aspect of Minishell's functionality. These modules work together cohesively to deliver seamless user experience. The following sections outline each module's purpose and functionality.

Module Descriptions

• Input module reads the user input and displays a prompt when waiting for a new command. This module uses the readline library, which provides line editing and command history capabilities. Custom signals required for the project are part of this module as well.
• Lexical Analysis module generates a list of tokens from the given input to be later used to break it down into an abstract syntax tree.
• Parser interprets the string of tokens and builds an AST.
• Execution unit executes the commands in the processed AST. This module handles built-ins, process creation, and process management. Additionally, it handles input/output redirection and pipelines, command lists, and subshell execution.
• Exit Status unit collects the exit status after execution, storing it in a special variable ?. It also cleans up the memory that is no longer in use.