Hive (42 School Network)

Minishell

Introduction

Minishell is a lightweight shell that's similar to standard Unix shells (like bash). It supports both interactive and non-interactive modes, signal handling, command history, built-in commands, and external executables with piping and redirection.

Table of Contents

• Features
  • Parser and command line prompt
  • Signals
  • Builtins
  • External commands
• Project structure
• Project diagram
• Installation

Features

Parser and command line prompt

Command line prompt and history

• This project uses readline library to show a prompt and capture user input.
• A working history of commands is maintained.

Parser

• It uses an AST (Abstract Syntax Tree) linked list to store user input.
• Tokenises input using special characters (|, <, >, <<, >>, $, etc.).
• Handles single (') and double quotes (") syntax.
• Checks for common syntax errors (e.g., unclosed quotes).
• Expands environment variables (using $ notation) and $? for the exit status of the last foreground command.

Signals

Signal handling
The shell supports the following key signals in both interactive and non-interactive modes:

Key	Interactive Mode	Non-Interactive Mode
Ctrl-C	Displays a new prompt.	Interrupts a running process
Ctrl-D	Exits the shell.	Signals EOF, ending input.
Ctrl-\	Does nothing (ignored).	Terminates process.

Builtins

Built-in commands are executed directly by the shell without calling external binaries. They follow the convention of returning '0' on success or a non-zero value on error (accessible via $?). Each builtin receives an array of strings as arguments (for example, "echo Hello!" is tokenized to ["echo", "Hello!", NULL] and then executed as builtin_echo(&args[1])).

Supported Built-ins:

• echo (supports -n option for omitting the newline)
• cd (changes the current working directory using relative or absolute paths)
• pwd (prints the current working directory)
• export (sets environment variables)
• unset (removes environment variables)
• env (displays the current environment)
• exit (exits the shell)

External commands

The shell can run external commands by searching the executable in the directories specified by the PATH variable.
Execution flow:

• Search for the executable in the PATH.
• Create a new process using fork() and execute the command with execve().

Piping and redirection:

• Pipe (|): support for piping output between processes.
• Redirections:
  • < redirects input.
  • > redirects output.
  • << reads input until a specified delimiter is encountered (here-document).
  • >> appends output.
• Supports combining here-documents (<<) with pipes.

Project structure

minishell/
│
├── libft/                    # Submodule libft
│
├── include/                  # Header files
│   ├── minishell.h
│   └── constants.h
│
├── src/                      # Source files
│   ├── builtins/
│   │   ├── utils/..
│   │   └── *.c
│   ├── constructor/
│   │   └── *.c
│   ├── destructor/
│   │   └── *.c
│   ├── environment/
│   │   └── *.c
│   ├── execution/
│   │   ├── utils/..
│   │   └── *.c
│   ├── parser/
│   │   └── *.c
│   ├── signals/
│   │   └── *.c
│   └── main.c
│
├── ...
└── Makefile                  # Building project tool

Project diagram

  

    

      
flowchart TD
    A1[Run ./minishell] --> B1[Initialization]
    B1 --> A2[Command Line Prompt]
    A2 --> B2[Syntax Validation]
    B2 --> C1{Is the line valid?}
    C1 --> |No| A2
    C1 --> |Yes| A3[Parsing]
    A3 --> A5[Here-document preprocessing]
    A5 --> A4[Execute Commands]

    subgraph Execute_Flow [Execute Flow]
        A4 --> C2{Is it a built-in?}
        C2 --> |Yes| A5[Execute Built-in Command]
        C2 --> |No| A6[Execute External Command]
        A5 --> C3{Is it 'exit'?}
    end

    C3 --> |No| A2
    C3 --> |Yes| B3[Exit Minishell]

    
  
  
    
      Loading

  

Installation

1. Clone the repository and build the project using the provided Makefile:

git clone https://github.com/kerito-cl/minishell.git
cd minishell
make

2. Run minishell:

./minishell

Other commands:
* make clean will remove all .o' files from the directory.
* make fclean will remove all .o' and executable files.
* make re will trigger the fclean command and rebuild the program.

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Made by Matias Quero and Julia Persidskaia.