Converting upper-case string into title-case using Ruby

"HELLO WORLD HOW ARE YOU".gsub(/\w+/) do |word|
  word.capitalize
end
#=> "Hello World How Are You"

If you're using Rails (really all you need is ActiveSupport, which is part of Rails), you can use titleize:

"MY STRING HERE".titleize
# => "My String Here"

If you're using plain Ruby but don't mind loading a small amount of ActiveSupport you can require it first:

require 'active_support/core_ext/string/inflections'
# => true
"MY STRING HERE".titleize
# => "My String Here"

N.B. By default titleize doesn't handle acronyms well and will split camelCaseStrings into separate words. This may or may not be desirable:

"Always use SSL on your iPhone".titleize
# => "Always Use Ssl On Your I Phone"

You can (partially) address this by adding "acronyms":

require 'active_support/core_ext/string/inflections' # If not using Rails
ActiveSupport::Inflector.inflections do |inflect|
  inflect.acronym 'SSL'
  inflect.acronym 'iPhone'
end
"Always use SSL on your iPhone".titleize
# => "Always Use SSL On Your IPhone"

For those who speak the Queen's English (or who struggle to spell titleize), there's no .titleise alias but you can use .titlecase instead.

While trying to come up with my own method (included below for reference), I realized that there's some pretty nasty corner cases. Better just use the method already provided in Facets, the mostest awesomest Ruby library evar:

require 'facets/string/titlecase'

class String
  def titleize
    split(/(\W)/).map(&:capitalize).join
  end
end

require 'test/unit'
class TestStringTitlecaseAndTitleize < Test::Unit::TestCase
  def setup
    @str = "i just saw \"twilight: new moon\", and man!   it's crap."
    @res = "I Just Saw \"Twilight: New Moon\", And Man!   It's Crap."
  end
  def test_that_facets_string_titlecase_works
    assert_equal @res, @str.titlecase
  end
  def test_that_my_own_broken_string_titleize_works
    assert_equal @res, @str.titleize # FAIL
  end
end

If you want something that more closely complies to typical writing style guidelines (i.e. does not capitalize words like "and"), there are a couple of "titleize" gems on GitHub.

From ActiveSupport

"MY STRING HERE".gsub(/\b('?[a-z])/) { $1.capitalize }

If you are using Rails/ActiveSupport, the method is already available for free.