String#count

str.count([other_str]+) -> integer

Returns: Integer · Updated March 13, 2026 · String Methods

strings counting characters

The count method counts how many times each character in the given sets appears in the string. It’s useful for quickly tallying character frequencies without writing explicit loops.

Syntax

str.count([other_str]+)

Parameters

Parameter	Type	Default	Description
`other_str`	`String`	—	One or more character sets to count. Each character in these strings increments the counter.

Examples

Basic character counting

hello = "hello world"
hello.count("l")
# => 3

hello.count("o")
# => 2

Counting multiple character sets

text = "hello HELLO"
text.count("A-Za-z")
# => 10

When you pass multiple strings, count finds the intersection of all character sets and counts only those characters.

"hello".count("hl", "l")
# => 2

"hello".count("lo", "el")
# => 2

Practical use case

def count_vowels(str)
  str.count("aeiouAEIOU")
end

count_vowels("hello world")
# => 3

Common Patterns

Character frequency analysis

def character_frequency(str)
  str.chars.uniq.each_with_object({}) do |char, freq|
    freq[char] = str.count(char)
  end
end

character_frequency("banana")
# => {"b"=>1, "a"=>3, "n"=>2}

Input validation

def contains_only_digits?(str)
  str.count("0-9") == str.length
end

contains_only_digits?("12345")  # => true
contains_only_digits?("12a45") # => false

Whitespace handling

sentence = "hello   world"
sentence.count(" ")    # => 5
sentence.count("\s")  # => 5 (includes tabs, newlines)

Errors

No special errors are raised. If an empty string is passed, the method returns 0.

"hello".count("")
# => 0