RainbowShell - Custom Unix Shell

Welcome to RainbowShell, my educational but powerful custom Unix shell written in C. RainbowShell implements pipes, redirections, logical operators, subshells, and background jobs while also featuring a rainbow/gradient greeting message (builtes color.h library).

Note: This is a project for the 3rd semester at CMC MSU (summarizing skills of systems programming, process handling, shell scripting concepts).

---

Table of Contents

• RainbowShell - Custom Unix Shell
  • Table of Contents
  • Features
  • Build
  • Usage
  • Project Structure
  • Examples
  • Background Jobs

---

Features

• Rainbow Greeting
  When you launch RainbowShell, you’re greeted with a colorful gradient welcome message. Because, who don't want to meet a rainbow 🌈 ?

• Custom Command Parser

  • Supports multi-stage pipelines: cmd1 | cmd2 | cmd3
  • Understands logical operators: &&, ||
  • Sequential execution: cmd1 ; cmd2
  • Subshells: (cd / && ls -l)
  • Redirections: < file, > file, >> file
  • Background tasks: cmd &

• Built-in Commands

  • cd <dir>: change directory (built-in, because changing directories in a child process has no effect on the parent)

• Error Handling

  • Lexer and parser produce meaningful, color-highlighted error messages (typos, missing quotes, etc).
  • Handles partial command failures in pipelines (ex. if the last command in a pipeline fails, subsequent && sections won’t run).

• Background Jobs

  • Run commands asynchronously with &.
  • Automatically ignores SIGINT (Ctrl-C) in the background job so it won’t be interrupted.
  • Prevents zombie processes via waitpid.

• Subshell & Grouping

  • Parentheses ( ... ) create a new job in a subshell.
    Example: (cd /; ls); pwd
  • You can group multiple commands, run them in the background, or combine with logical operators.

• Extensible Architecture

  • Separation of lexer, parser, and executor.
  • Because of it future features or built-ins can be easily added.

---

Build

1. Clone this repository:

   git clone https://github.com/estnafinema0/RainbowShell.git
   cd RainbowShell/shell

2. Compile using make:

   make

   Now we have executable Rainbowshell.

3. Run RainbowShell:

   ./Rainbowshell

---

Usage

Now you are open to type any commands as in a standard Unix shell.

shell> echo "Hello World"

Use Ctrl-C to send an interrupt signal to foreground commands. If a command is run in the background (using &), it won’t be interrupted by Ctrl-C (as it should be in a usual shell!).

---

Project Structure

• main.c
  Entry point for RainbowShell. Handles signals (SIGINT and SIGCHLD), prints the rainbow greeting, and starts the main interactive loop.

• parser.c / parser.h
  Contains the logic for parsing command lines into a structured form (Job and Command objects). Handles operators like &&, ||, |, ;, &, as well as subshell grouping ( ... ).

• lexer.c / lexer.h
  Breaks the command line into tokens (TOKEN_WORD, TOKEN_OPERATOR, etc.). Also handles quoted strings and error checking for unclosed quotes.

• executor.c / executor.h
  Executes commands by forking processes. Implements:

  • Pipelines (|)
  • Sequential commands (;)
  • Conditional commands (&&, ||)
  • Subshells
  • Redirections (<, >, >>)
  • Background jobs (&)

• builtins.c / builtins.h
  Built-in commands such as cd.

• colors.c / colors.h
  Provides color/gradient print utilities. The print_rainbow_text function produces the signature rainbow greeting.

• structures.h
  Defines the primary data structures (Command, Job, OperatorType) used across the shell.

• makefile
  Contains build rules. Simply run make.

---

Examples

Here are some commands to showcase RainbowShell’s broad functionality:

1. Subshell & Sequential

   (cd /; pwd); pwd

   • Changes directory to /, prints it, then returns to the parent shell and prints its current directory.

2. Conditional Execution

   (false && echo "Skipped 1") || (echo "Fallback 1" && echo "Part of fallback")

   • false fails, so && chain is skipped; || triggers the fallback commands.

3. Background Task with Redirection

   echo "Background task" > output.txt & cat output.txt

   • The echo runs in the background, while the shell immediately proceeds to cat output.txt.

4. Pipeline

   echo "hello" | grep "hello" && echo "Pipeline succeeded" || echo "Pipeline failed"

   • If grep "hello" finds the text, the && chain continues.

5. Multiple Steps with Conditionals

   ls non_existent_dir && echo "This should not print" || echo "Directory not found"

   • Fails on the nonexistent directory, triggers the || fallback.

6. Process Listing and Subshell

   ps; ls; (cd .. ; ls; ps) && ls && ps

   • Shows how a subshell can change directory without affecting the parent shell.

7. Background Sleep

   sleep 5 & echo "Background process test"

   • sleep runs in the background, while RainbowShell continues to the next command.

---

Background Jobs

If you type & in the end of the command, it will launch in the background:

• Non-blocking background: The shell is immediately ready for the next command.
• No Zombie Processes: RainbowShell calls waitpid appropriately.
• Ignored SIGINT: Background jobs ignor Ctrl-C from the main terminal.

---

Thank you for checking out RainbowShell! Enjoy the rainbow!🌈