Capture groups in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a capture group in Ruby regular expressions?

A capture group is a part of a regular expression enclosed in parentheses (). It saves the matched text so you can use it later.

beginner

How do you access the text matched by the first capture group in Ruby?

You can access it using $1 after the match or by using MatchData[1] if you use =~ or match methods.

beginner

What does this Ruby code output?<br>

text = 'Name: John'
if text =~ /Name: (\w+)/
  puts $1
end

It outputs John because the capture group (\w+) matches the word after 'Name: ' and $1 holds that match.

intermediate

Can capture groups be nested in Ruby regular expressions?

Yes, capture groups can be nested. Each pair of parentheses creates a new group, and you can access them by their order of opening parentheses.

intermediate

What is the difference between a capture group and a non-capturing group in Ruby regex?

A capture group saves the matched text for later use. A non-capturing group, written as (?:...), groups parts of the pattern without saving the match.

In Ruby, what does the capture group (\d+) match?

A One or more digits

B One or more letters

C Any character except digits

D Exactly one digit

The pattern \d+ matches one or more digits (0-9).

How do you write a non-capturing group in Ruby regex?

A [pattern]

B (?:pattern)

C (pattern)

D {pattern}

Non-capturing groups use (?:...) to group without saving the match.

After matching with /Hello (\w+)/, how do you get the captured word in Ruby?

A $1

B $0

C match[0]

D match[2]

$1 holds the text matched by the first capture group.

What will /(a(b))/.match('ab')[2] return in Ruby?

A nil

B ab

C a

D b

The second capture group (b) matches 'b', so match[2] returns 'b'.

Which of these is true about capture groups in Ruby regex?

A They change the original string

B They only match digits

C They save matched text for later use

D They cannot be nested

Capture groups save the matched text so you can use it later in your code.

Explain what a capture group is and how you use it in Ruby regular expressions.

Think about how parentheses help you save parts of the matched text.

Describe the difference between a capturing group and a non-capturing group in Ruby regex.

One saves the match, the other just groups without saving.