Why regex is powerful in Ruby - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the string contains the word 'Ruby'.

Ruby

text = "I love programming in Ruby"
puts text =~ /[1]/ ? "Found" : "Not found"

Drag options to blanks, or click blank then click option'

ARuby

BPython

CJava

DC++

Attempts:

3 left

💡 Hint

Common Mistakes

Using a word not present in the string, causing no match.

The regex /Ruby/ matches the word 'Ruby' in the string, so the output is 'Found'.

2fill in blank

medium

Complete the code to find all words starting with 'b' in the string.

Ruby

text = "bat ball cat box"
matches = text.scan(/[1]\w*/)
puts matches.join(", ")

Drag options to blanks, or click blank then click option'

Ad

Bc

Ca

Db

Attempts:

3 left

💡 Hint

Common Mistakes

Using a letter that does not match any word start.

The regex /b\w*/ matches words starting with 'b'. The output will be 'bat, ball, box'.

3fill in blank

hard

Fix the error in the regex to match an email address.

Ruby

email = "[e-mail]"
puts email.match(/\A[\w.+-]+@[1]\.[a-z]{2,}\z/i) ? "Valid" : "Invalid"

Drag options to blanks, or click blank then click option'

A[a-z]+

B[0-9]+

C[a-z0-9-]+

D[A-Z]+

Attempts:

3 left

💡 Hint

Common Mistakes

Using only letters or digits, missing hyphens in domain.

The regex part [a-z0-9-]+ correctly matches domain names with letters, digits, and hyphens.

4fill in blank

hard

Fill both blanks to create a regex that matches a date in 'YYYY-MM-DD' format.

Ruby

date = "2024-06-15"
pattern = /\A[1]-[2]-\d{2}\z/
puts date.match?(pattern) ? "Date valid" : "Date invalid"

Drag options to blanks, or click blank then click option'

A\d{4}

B\d{2}

C[a-z]{4}

D[0-9]{3}

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong digit counts or letters instead of digits.

The regex \d{4}-\d{2}-\d{2} matches dates like '2024-06-15' with four digits year and two digits month and day.

5fill in blank

hard

Fill all three blanks to create a hash that maps words to their lengths only if length is greater than 3.

Ruby

words = ["ruby", "is", "fun", "and", "powerful"]
lengths = { [1]: [2] for [3] in words if [2] > 3 }

Drag options to blanks, or click blank then click option'

Aword

Blen(word)

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or missing the length condition.

The hash comprehension uses 'word' as key, 'len(word)' as value, iterating over 'word' in words, filtering length > 3.

Practice

1. Why is regex considered powerful in Ruby?

easy

A. It cannot be combined with other Ruby methods.

B. It only works with numbers, not text.

C. It requires complex syntax to use.

D. It can quickly find and manipulate text patterns.

Solution

1. Step 1: Understand regex purpose in Ruby

   Regex is used to find patterns in text efficiently.

2. Step 2: Recognize Ruby's regex flexibility

   Ruby allows easy pattern matching and text manipulation using regex.

3. Final Answer:

   It can quickly find and manipulate text patterns. -> Option D

4. Quick Check:

   Regex power = quick text pattern handling [OK]

Hint: Regex helps find text patterns fast in Ruby [OK]

Common Mistakes:

• Thinking regex only works with numbers
• Believing regex syntax is always complex
• Assuming regex can't be combined with Ruby methods

2. Which of the following is the correct way to write a regex literal in Ruby?

easy

A. /pattern/

B. 'pattern'

C. {pattern}

D. (pattern)

Solution

1. Step 1: Identify Ruby regex syntax

   Ruby uses slashes / / to define regex literals.

2. Step 2: Compare options

   Only /pattern/ matches Ruby regex literal syntax.

3. Final Answer:

   /pattern/ -> Option A

4. Quick Check:

   Regex literal = /pattern/ [OK]

Hint: Regex literals in Ruby use slashes /pattern/ [OK]

Common Mistakes:

• Using quotes instead of slashes
• Using braces or parentheses for regex
• Confusing regex with string syntax

3. What will be the output of this Ruby code?

text = "hello123"
match = text.match(/\d+/)
puts match[0]

medium

A. hello

B. 123

C. nil

D. error

Solution

1. Step 1: Understand the regex /\d+/

   This regex matches one or more digits in the string.

2. Step 2: Apply regex to text "hello123"

   The digits "123" match the pattern and are captured.

3. Final Answer:

   123 -> Option B

4. Quick Check:

   Digits found = 123 [OK]

Hint: \d+ matches digits; here it finds '123' [OK]

Common Mistakes:

• Expecting 'hello' as output
• Thinking match returns nil if partial match exists
• Confusing match object with string

4. Find the error in this Ruby code using regex:

text = "abc123"
if text =~ /\d+/
  puts "Digits found"
else
  puts "No digits"
end

medium

A. The regex syntax is incorrect

B. The =~ operator is used wrongly

C. No error; code works as expected

D. Missing parentheses in if condition

Solution

1. Step 1: Check regex syntax

   The regex /\d+/ correctly matches digits.

2. Step 2: Verify use of =~ operator

   The =~ operator checks if regex matches the string; usage is correct.

3. Final Answer:

   No error; code works as expected -> Option C

4. Quick Check:

   Regex and operator usage = correct [OK]

Hint: =~ checks regex match; no parentheses needed [OK]

Common Mistakes:

• Thinking =~ is invalid operator
• Expecting parentheses required in if
• Assuming regex syntax is wrong

5. How can you use regex in Ruby to replace all vowels in a string with '*'?

hard

A. string.gsub(/[aeiou]/i, '*')

B. string.replace(/[aeiou]/, '*')

C. string.sub(/[aeiou]/, '*')

D. string.match(/[aeiou]/).replace('*')

Solution

1. Step 1: Identify method to replace all matches

   gsub replaces all occurrences matching regex in the string.

2. Step 2: Use regex for vowels with case-insensitive flag

   /[aeiou]/i matches all vowels regardless of case.

3. Step 3: Combine to replace vowels with '*'

   string.gsub(/[aeiou]/i, '*') replaces all vowels with '*'.

4. Final Answer:

   string.gsub(/[aeiou]/i, '*') -> Option A

5. Quick Check:

   Replace vowels = gsub with /[aeiou]/i [OK]

Hint: Use gsub with /[aeiou]/i to replace all vowels [OK]

Common Mistakes:

• Using sub replaces only first match
• Using replace method incorrectly
• Trying to call replace on match object