ruby - How do I count vowels?

Question

I've seen the solution and it more or less matches

Write a method that takes a string and returns the number of vowels
 in the string. You may assume that all the letters are lower cased. You can treat "y" as a consonant.
Difficulty: easy.

def count_vowels(string)
    vowel = 0
    i = 0
    while i < string.length  
        if (string[i]=="a" || string[i]=="e" || string[i]=="i" || string[i]=="o"|| string[i]=="u")
            vowel +=1
end

    i +=1

return vowel

end

puts("count_vowels("abcd") == 1: #{count_vowels("abcd") == 1}")
puts("count_vowels("color") == 2: #{count_vowels("color") == 2}")
puts("count_vowels("colour") == 3: #{count_vowels("colour") == 3}")
puts("count_vowels("cecilia") == 4: #{count_vowels("cecilia") == 4}")

Answer 1

def count_vowels(str)
  str.scan(/[aeoui]/).count
end

/[aeoui]/ is a regular expression that basically means "Any of these characters: a, e, o, u, i". The String#scan method returns all matches of a regular expression in the string.