Strings in Ruby

Mutable text with rich methods and encoding support.

Basics and interpolation

Double quotes interpolate; single quotes do not (except \ and \').

name = "Ruby"
"Hello, #{name}!"  # => "Hello, Ruby!"
'Hello, #{name}!'   # => "Hello, \\#{name}!"

Encodings and length

Ruby strings are encoding‑aware (UTF‑8 by default). length counts characters (codepoints); bytesize counts bytes.

"résumé".encoding   # => #<Encoding:UTF-8>
"résumé".length     # => 6
"résumé".bytesize   # => 8

Common operations

"  hi ".strip               # => "hi"
"a,b,c".split(",")         # => ["a","b","c"]
"test".gsub("t", "T")       # => "TesT"
"go" * 3                    # => "gogogo"
"path/to" + "/file"        # concatenation
["a","b"].join("-")        # => "a-b"

Mutation and freezing

Strings are mutable; bang methods modify in place. Freeze to make immutable.

s = "hello"
s.upcase!    # => "HELLO" (s mutated)
s << "!"     # append
s.freeze
# s << "!"  # would raise FrozenError

Substrings and indexing

s = "hello"
s[0]        # => "h"
s[1,3]      # => "ell"
s[0..1]     # => "he"

Regex integration

match, scan, sub/gsub integrate with regular expressions.

"a1 b22".scan(/\d+/)           # => ["1", "22"]
"color".sub(/or/, "our")      # => "colour"
"a1 b2".gsub(/\d+/) { |d| (d.to_i * 2).to_s }  # => "a2 b4"

Heredoc

Convenient multi‑line literals; squiggly heredoc strips indentation.

message = <<~TEXT
  Hello,
    world.
TEXT

Performance notes

• Prefer string interpolation ("#{x}") over concatenation in loops
• Use StringIO for building large strings incrementally

Summary

• Use double quotes for interpolation, single for literals
• Strings are mutable by default; freeze when sharing or for safety
• Understand encodings when slicing and measuring