23. Build a Simple Template Engine
1. Hello, World!
2. Rename Photos by Capture Date
3. Organize Downloads Folder by File Type
4. Delete Old Log Files Automatically
5. Find Duplicate Files Using MD5 Hashing
6. Generate Comprehensive File Inventory
7. Parse Web Server Logs for Performance Metrics
8. Extract Emails, URLs, and Phone Numbers from Text
9. Track Daily and Monthly Active Users from Apache Logs
10. Generate Formatted Text Reports with Column Alignment
11. Analyze Sales Transactions and Generate Revenue Reports
12. Clean and Validate CSV Data
13. Convert JSON API Responses to CSV
14. Parse and Validate Configuration Files
15. Build a CLI Calculator with Argument Parsing
16. Parse and Display Weather Data from JSON
17. Build a Simple Inventory System with Classes
18. Generate Markdown Table from CSV Data
19. Aggregate Sales Data by Time Period
20. Recursive Directory Size Calculator with Filtering
21. Parse and Transform Server Configuration
22. Find and Replace Across Multiple Files
23. Build a Simple Template Engine
24. CSV Data Validator with Business Rules
25. Build a Multi-Format Log Analyzer

Challenge

Problem

Template engines power web frameworks, email systems, and code generators by dynamically inserting data into predefined structures. This drill teaches you to parse template syntax, substitute variables, handle loops, and generate dynamic content. You'll learn pattern matching with regular expressions, string manipulation, and data binding—essential skills for building web applications, code generators, and automation tools.

Difficulty: Intermediate

Instructions

  1. Read template string and data hash
  2. Process template directives:
    • Variables: {{variable_name}} - replace with value from data
    • Loops: {{#each items}}{{this}}{{/each}} - repeat for each item in array
  3. Handle nested data: {{user.name}} accesses nested hash values
  4. Handle missing variables gracefully (replace with empty string)
  5. Return the rendered output string

Files

Editable

Hints

Hint 1

Use String#gsub with regex and block to process patterns

Hint 2

Regex for variables: /{{([\w.]+)}}/

Hint 3

Regex for each loops: /{{#each (\w+)}}(.*?){{/each}}/m

Hint 4

The /m flag enables multiline matching

Hint 5

Capture groups are accessed with $1, $2, etc.

Hint 6

Non-greedy match: .*? matches minimum characters

Hint 7

Split nested path: 'user.name'.split('.') => ['user', 'name']

Ruby 3.4

1. Simple variable substitution

Input: 
template = "Hello {{name}}!"
data = {'name' => 'Alice'}
puts render_template(template, data)
Expected Output: 
Hello Alice!

2. Loop through array

Input: 
template = "Items: {{#each items}}{{this}} {{/each}}"
data = {'items' => ['a', 'b', 'c']}
puts render_template(template, data)
Expected Output: 
Items: a b c

3. Nested data access

Input: 
template = "User: {{user.name}}, Age: {{user.age}}"
data = {'user' => {'name' => 'Bob', 'age' => 30}}
puts render_template(template, data)
Expected Output: 
User: Bob, Age: 30

4. Missing variable returns empty

Input: 
template = "Hello {{name}}! Your score: {{score}}"
data = {'name' => 'Carol'}
puts render_template(template, data)
Expected Output: 
Hello Carol! Your score:
+ 2 hidden test cases