🐚 rush — Rapid Unix Shell (C)

rush is a lightweight Unix shell written in C that implements core shell functionality including command execution, built-in commands, redirection, and parallel processing.

The goal of this project is to demonstrate process management, system calls, and command parsing in a Unix/Linux environment.

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📌 Overview

rush is a command-line interpreter that repeatedly:

1. Displays a prompt
2. Reads user input
3. Parses the command
4. Executes the command
5. Waits for completion
6. Repeats until the user exits

Example prompt:

rush>

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✨ Features

• Command prompt and execution loop
• Built-in commands: exit, cd, path
• Executable path resolution
• Output redirection (>)
• Parallel command execution (&)
• Robust error handling
• Flexible whitespace parsing

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🏗️ Project Structure

.
├── makefile
├── rush.c
└── README.md

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⚙️ Build Instructions

Requirements

• Linux environment
• GCC

Compile

make

This produces the executable:

./rush

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▶️ Running the Shell

./rush

You will see:

rush>

Type commands just like a normal Unix shell.

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🧠 How It Works

Command Execution

External commands are executed using:

• fork() — create child process
• execv() — run the program
• wait() / waitpid() — wait for completion

The shell searches for executables using directories defined in the path list.

Default path:

/bin

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🔧 Built-in Commands

exit

Exits the shell.

rush> exit

Rules:

• No arguments allowed.

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cd <directory>

Changes the current working directory.

rush> cd /tmp

Rules:

• Must receive exactly one argument.

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path [dir1 dir2 ...]

Sets the executable search path.

rush> path /bin /usr/bin

Clear the path:

rush> path

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📤 Output Redirection

Redirect command output using >:

rush> ls -la > files.txt

Behavior:

• Output file is created if it does not exist
• Existing files are overwritten
• Errors during file creation are reported

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⚡ Parallel Execution

Use & to run commands simultaneously:

rush> sleep 1 & ls & echo done

The shell waits until all commands finish before showing the next prompt.

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❗ Error Handling

All errors print a single message to stderr:

An error has occurred

The shell continues running after most errors.

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🧪 Example Session

rush> path /bin
rush> ls
rush> cd /tmp
rush> ls > output.txt
rush> sleep 1 & echo hello & ls
rush> exit