Capture groups in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of capture groups in Ruby regex

What is the output of this Ruby code snippet?

Ruby

text = "Name: John, Age: 30"
match = /Name: (\w+), Age: (\d+)/.match(text)
puts match[1]
puts match[2]

A John\n30

B Name\nAge

C John, Age: 30

D nil\nnil

💡 Hint

Remember that capture groups are accessed by their index starting at 1.

The regex captures the word after 'Name: ' as group 1 and the digits after 'Age: ' as group 2. match[1] returns 'John' and match[2] returns '30'.

❓ Predict Output

intermediate

Using named capture groups in Ruby

What will this Ruby code print?

Ruby

text = "Product: Book, Price: 15"
regex = /Product: (?<product>\w+), Price: (?<price>\d+)/
match = regex.match(text)
puts match[:product]
puts match[:price]

A product\nprice

B Book\n15

C Book, Price: 15

D nil\nnil

💡 Hint

Named capture groups can be accessed by symbol keys.

The named groups 'product' and 'price' capture 'Book' and '15' respectively. Accessing match[:product] and match[:price] prints these values.

❓ Predict Output

advanced

Accessing a capture group index beyond available groups

What does this Ruby code print?

Ruby

text = "Date: 2024-06-15"
match = /Date: (\d{4})-(\d{2})-(\d{2})/.match(text)
p match[4]

A IndexError

B TypeError

C nil

D NoMethodError

💡 Hint

Check how many capture groups are in the regex and the index used.

The regex has 3 capture groups, so match[4] returns nil. `p nil` prints 'nil'.

🧠 Conceptual

advanced

Effect of non-capturing groups on match data

Given the regex /a(?:b)c(d)/ applied to the string "abcd", how many capture groups does the match have?

A 0

B 2

C 3

D 1

💡 Hint

Non-capturing groups do not count as capture groups.

The (?:b) is a non-capturing group, so only (d) counts as a capture group, total 1.

❓ Predict Output

expert

Output of nested capture groups in Ruby

What is the output of this Ruby code?

Ruby

text = "abc123xyz"
regex = /(a(b(c)))(\d+)(x(y)z)/
match = regex.match(text)
puts match[0]
puts match[1]
puts match[2]
puts match[3]
puts match[4]
puts match[5]
puts match[6]

A abc123xyz\nabc\nbc\nc\n123\nxyz\ny

B abc123xyz\nabc\nbc\nc\n123\nxyz\nnil

C abc123xyz\nabc\nbc\nnil\n123\nxyz\ny

D abc123xyz\nabc\nnil\nc\n123\nxyz\ny

💡 Hint

Nested capture groups are numbered from left to right by their opening parenthesis.

The groups are: 0=full match, 1=(a(b(c))), 2=(b(c)), 3=(c), 4=(\d+), 5=(x(y)z), 6=(y). The output prints each group accordingly.