String

String.new, String()

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

strings text characters encoding

The String class is fundamental to Ruby, representing sequences of characters. Ruby’s strings are versatile, mutable, and natively support UTF-8 encoding.

Creating Strings

# Literals
"hello"           # => "hello"
'hello'           # => "hello" (no interpolation)
%q{hello}         # => "hello"
%Q{hello #{world}} # => "hello world"

# Constructor
String.new("hello")  # => "hello"
String(42)           # => "42"

String Methods

Querying

"hello".length      # => 5
"hello".size        # => 5
"hello".empty?      # => false
"".empty?           # => true
"hello".bytesize   # => 5 (UTF-8 bytes)

Modification

# Concatenation
"hello" + " world"   # => "hello world"
"hello" << " world"  # => "hello world" (mutating)
"hello" * 3          # => "hellohellohello"

Case Conversion

"HELLO".downcase   # => "hello"
"hello".upcase     # => "HELLO"
"Hello".capitalize # => "Hello"
"HeLLo".swapcase   # => "hEllO"

Searching and Replacing

"hello".include?("ll")   # => true
"hello".index("ll")      # => 2
"hello".start_with?("he") # => true
"hello".end_with?("lo")  # => true
"hello".gsub("l", "r")   # => "herro"

Encoding

# Default UTF-8
"hello".encoding  # => #<Encoding:UTF-8>

# Convert encoding
"hello".encode("ASCII")    # => "hello"
"héllo".encode("ASCII", invalid: :replace)  # => "?ll?"

Practical Examples

Splitting and Joining

"a,b,c".split(",")      # => ["a", "b", "c"]
["a", "b", "c"].join("-") # => "a-b-c"

Stripping Whitespace

"  hello  ".strip       # => "hello"
"hello\n".chomp         # => "hello"

Interpolation

name = "World"
"Hello, #{name}!"       # => "Hello, World!"

Multiline Strings

# Heredoc
text = <<~TEXT
  This is a multiline
  string in Ruby
TEXT

# % notation
text = <<-TEXT
  Indented heredoc
TEXT

Mutable Strings

Unlike some languages, Ruby strings are mutable:

str = "hello"
str << " world"  # Mutates: "hello world"
str.upcase!      # Mutates: "HELLO"

String Encoding Issues

# Force encoding
str = "hello".force_encoding("UTF-8")

# Valid encoding check
"hello".valid_encoding?  # => true

The String class provides extensive functionality for text processing, making Ruby excellent for tasks involving string manipulation.