Common patterns and character classes in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby regex match?

Consider the following Ruby code snippet. What will be printed when it runs?

Ruby

text = "Email: [e-mail]"
match = text.match(/\b\w+@\w+\.\w+\b/)
puts match[0]

A Email

B nil

C example.com

D [e-mail]

💡 Hint

Look for the pattern that matches an email-like string.

The regex \b\w+@\w+\.\w+\b matches a word boundary, then one or more word characters, an '@', more word characters, a dot, and word characters again. It matches the email part in the string.

❓ Predict Output

intermediate

What does this regex find in the string?

Given the Ruby code below, what will be the output?

Ruby

text = "Call me at 123-456-7890 or 987-654-3210."
numbers = text.scan(/\d{3}-\d{3}-\d{4}/)
puts numbers.join(", ")

A Call, me, at

B 1234567890, 9876543210

C 123-456-7890, 987-654-3210

D []

💡 Hint

Look for the pattern matching phone numbers with dashes.

The regex \d{3}-\d{3}-\d{4} matches three digits, a dash, three digits, a dash, and four digits, which matches the phone numbers in the string.

🔧 Debug

advanced

Why does this regex fail to match?

The following Ruby code is intended to find all words starting with a capital letter. Why does it not find any matches?

Ruby

text = "I."
matches = text.scan(/[A-Z][a-z]+/)
puts matches

A It misses single-letter capital words like 'I' because the pattern requires at least one lowercase letter after the capital letter.

B The regex is case-insensitive by default, so it matches everything.

C The pattern uses wrong character classes; it should use \w instead of [a-z].

D The scan method returns nil if no matches are found.

💡 Hint

Check what the pattern requires after the capital letter.

The regex [A-Z][a-z]+ matches a capital letter followed by one or more lowercase letters. Single capital letters like 'I' have no lowercase letters after them, so they are not matched.

📝 Syntax

advanced

Which regex pattern correctly matches a hexadecimal color code?

You want to match strings like '#1a2b3c' or '#ABCDEF' in Ruby. Which pattern is correct?

A /#([0-9a-fA-F]{6})\b/

B /#([0-9g-zA-Z]{6})/

C /#([0-9a-f]{6})/i

D /#([0-9a-fA-F]{3,6})/

💡 Hint

Hex digits are 0-9 and a-f (case insensitive).

Option A matches a '#' followed by exactly 6 hex digits (0-9, a-f, A-F) and a word boundary. Option A is case-insensitive but misses the word boundary and is less precise. Option A includes invalid characters 'g-z'. Option A allows 3 to 6 digits, which is not strictly a 6-digit hex code.

🚀 Application

expert

How many matches does this regex find?

In Ruby, given the string and regex below, how many matches will be found?

Ruby

text = "abc123xyz456def789"
matches = text.scan(/[a-z]+\d+/)
puts matches.size

A 1

B 3

C 0

D 2

💡 Hint

Look for sequences of letters followed immediately by digits.

The regex [a-z]+\d+ matches one or more lowercase letters followed by one or more digits. The string has 'abc123', 'xyz456', and 'def789' matching this pattern, so 3 matches.