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 XML Configuration Files
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 conditionals, and generate dynamic content. You'll learn pattern matching with regular expressions, recursive parsing, string interpolation, and data binding—essential skills for building web applications, code generators, and automation tools.

Difficulty: Intermediate

Instructions

  1. Read template from template.txt
  2. Read data from data.json (contains hash of variable values)
  3. Process template directives:
    • Variables: {{variable_name}} - replace with value from data
    • If statements: {{#if variable}}content{{/if}} - show content if variable is truthy
    • Loops: {{#each items}}{{this}}{{/each}} - repeat for each item in array
  4. Handle nested data: {{user.name}} accesses nested hash values
  5. Handle missing variables gracefully (replace with empty string)
  6. Write rendered output to output.txt
  7. Print confirmation: 'Template rendered successfully'
  8. Exit with status 1 if template syntax errors

Files

Editable
Read-only

Hints

Hint 1

Use String#gsub with regex and block to process patterns

Hint 2

Regex /pattern/m enables multiline matching

Hint 3

Capture groups: /{{(\w+)}}/ captures variable name in $1

Hint 4

Non-greedy match: .*? matches minimum characters

Hint 5

Check truthiness: value && value != false

Hint 6

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

Hint 7

Navigate hash: keys.each { |k| value = value[k] }

Hint 8

Replace {{this}} in loop: string.gsub('{{this}}', item)

Provided Files (Read-only)

1. Simple variable substitution

Input: 
render_template('template.txt', 'data.json', 'output.txt')
Expected Output: 
Template rendered successfully

2. Loop through array

Input: 
render_template('template.txt', 'data.json', 'output.txt')
Expected Output: 
Template rendered successfully

3. Conditional if statement

Input: 
render_template('template.txt', 'data.json', 'output.txt')
Expected Output: 
Template rendered successfully

4. Nested data access

Input: 
render_template('template.txt', 'data.json', 'output.txt')
Expected Output: 
Template rendered successfully
+ 3 hidden test cases