PING — Your First Redis Command

Welcome to Build Redis from Scratch! In this project course, you'll implement a working Redis clone step by step, starting from the simplest possible command.

What is Redis?

Redis is an in-memory data structure store used as a database, cache, and message broker. It's one of the most popular databases in the world — used by Twitter, GitHub, Stack Overflow, and thousands of other companies.

What makes Redis special:

• Blazing fast: All data lives in RAM. Operations complete in microseconds.
• Rich data types: Not just key-value — Redis supports strings, lists, sets, sorted sets, hashes, and more.
• Simple protocol: The Redis Serialization Protocol (RESP) is human-readable and easy to implement.

The RESP Protocol

Redis clients and servers communicate using RESP (Redis Serialization Protocol). Every response has a type prefix as its first byte:

Every piece ends with \r\n (carriage return + line feed).

The PING Command

PING is the simplest Redis command. It's used to test if the server is alive.

• PING → +PONG\r\n (simple string response)
• PING hello → $5\r\nhello\r\n (bulk string echo)

A bulk string encodes the length first: $<length>\r\n<data>\r\n

Your Task

Build a program that:

1. Reads commands from stdin (one per line)
2. Parses the command name and arguments
3. For PING, writes the correct RESP response to stdout

This is the foundation everything else builds on. Let's go!