Gsub with regex in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of gsub with regex replacing digits

What is the output of this Ruby code?

text = "Room 123, Floor 4"
result = text.gsub(/\d+/, "#")
puts result

Ruby

text = "Room 123, Floor 4"
result = text.gsub(/\d+/, "#")
puts result

A Room #, Floor #

B Room 123, Floor 4

C Room #23, Floor #

D Room , Floor

💡 Hint

The regex /\d+/ matches one or more digits in a row.

The gsub method replaces all sequences of digits (\d+) with the string '#'. So '123' and '4' are replaced separately.

❓ Predict Output

intermediate

Replacing vowels with '*' using gsub and regex

What will this Ruby code print?

sentence = "Hello World"
output = sentence.gsub(/[aeiou]/i, '*')
puts output

Ruby

sentence = "Hello World"
output = sentence.gsub(/[aeiou]/i, '*')
puts output

A Hello World

B H*ll* W*rld

C H*ll* W*rld*

D *e**o *o*l*

💡 Hint

The regex matches vowels ignoring case, replacing each vowel with '*'.

The regex /[aeiou]/i matches vowels regardless of case. Each vowel is replaced by '*'.

❓ Predict Output

advanced

Using gsub with regex and block to double digits

What is the output of this Ruby code?

str = "a1b2c3"
result = str.gsub(/\d/) { |d| (d.to_i * 2).to_s }
puts result

Ruby

str = "a1b2c3"
result = str.gsub(/\d/) { |d| (d.to_i * 2).to_s }
puts result

A a0b0c0

B a1b2c3

C a12b24c36

D a2b4c6

💡 Hint

The block doubles each digit found by the regex.

The regex matches each digit. The block converts it to integer, doubles it, then converts back to string for replacement.

❓ Predict Output

advanced

Effect of gsub with regex and anchors

What will this Ruby code output?

text = "start middle end"
new_text = text.gsub(/^start/, "begin")
puts new_text

Ruby

text = "start middle end"
new_text = text.gsub(/^start/, "begin")
puts new_text

A middle end

B begin middle begin

C begin middle end

D start middle end

💡 Hint

The ^ anchor matches the start of the string only.

The regex /^start/ matches 'start' only at the beginning of the string and replaces it with 'begin'.

❓ Predict Output

expert

Complex gsub with regex and capture groups

What is the output of this Ruby code?

text = "abc123xyz456"
result = text.gsub(/(\D+)(\d+)/) { |match| $1.reverse + ($2.to_i + 1).to_s }
puts result

Ruby

text = "abc123xyz456"
result = text.gsub(/(\D+)(\d+)/) { |match| $1.reverse + ($2.to_i + 1).to_s }
puts result

A cba124zyx457

B abc124xyz457

C cba123zyx456

D abc123xyz456

💡 Hint

The regex captures letters and digits separately; letters are reversed, digits incremented by 1.

The regex /(\D+)(\d+)/ matches groups of letters and digits. The block reverses the letters and adds 1 to the digits before joining.