Project 1: A Smarter grep with Ranges

A command-line tool that searches for a given text pattern in files. It will be more powerful than a simple grep because you’ll use D’s ranges to chain operations, like searching only in certain line numbers or filtering by length.

Quick Reference

Attribute Value
Primary Language D
Alternative Languages N/A
Difficulty Level 1: Beginner
Time Estimate Weekend
Knowledge Area Standard Library / Functional Programming
Tooling dub, Phobos (D Standard Library)
Prerequisites Basic programming knowledge in any C-style language.

What You Will Build

A command-line tool that searches for a given text pattern in files. It will be more powerful than a simple grep because you’ll use D’s ranges to chain operations, like searching only in certain line numbers or filtering by length.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Setting up a dub project → maps to using dub init and understanding dub.json or dub.sdl
  • Reading command-line arguments → maps to working with std.stdio and std.getopt
  • Reading a file lazily → maps to using std.file.File("path").byLine
  • Chaining range algorithms → maps to using filter, map, and enumerate to build a processing pipeline

Key Concepts

  • D’s Standard Library (Phobos): “Programming in D” - Part III.
  • Ranges: “Programming in D” - Chapter 12.
  • dub: The official dub documentation.

Real-World Outcome

# Your tool in action
> ./dgrep "Error" log.txt | head -n 5
[2023-10-27 10:15:00] Error: Connection timed out.
[2023-10-27 10:15:05] Error: Failed to resolve host.

# Chain operations, thanks to ranges and UFCS
> ./dgrep "Error" log.txt | grep "resolve"
[2023-10-27 10:15:05] Error: Failed to resolve host.

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: LEARN_D_PROGRAMMING_LANGUAGE.md
  • “Programming in D” by Ali Çehreli