Build your own grep from scratch. Read stdin, filter text by pattern and handle exit codes while learning the foundations of Unix tools.
Build it in your language
The tester treats your program as a black box: any language works. These are just the most convenient ones for this project.
Project in preparation: we are completing and verifying the implementation path and its tests. The capabilities below describe the project goal; starting the project is not enabled yet.
grep is the perfect Unix tool: it does one thing, it does it fast, and it composes with everything else. Rebuilding it teaches as much about design philosophy as it does about code.
You'll build a clone that searches by pattern in stdin and in files, with the flags you actually use (-i, -v, -n, -c, -r), and with correct behaviour in the part nobody looks at but everybody depends on: exit codes.
7 stages across 3 phases. Every stage comes with its guide and its tests: you move on when they pass.
Read stdin, search for a literal string and print the matches.
-i, -v, -n, -c, several files at once, and correct exit codes.
Character classes, anchors and recursive directory search.
Build a coding agent from scratch. Connect models through OpenRouter, secure API keys, define tools and implement the autonomous ReAct loop.
Python · TypeScript
Build your own Git from scratch. Store blobs, trees and commits to understand content-addressed objects and how version control works.
Go · Python · Rust