Ruby strings have methods to convert them to uppercase and lowercase. The method names of the methods are upcase and downcase respectively.

Calling the downcase or upcase method on a string will return the lowercase or uppercase version of the string, but the original variable won't change. 

name = 'Ruby'
puts name           # Ruby
puts name.downcase  # ruby
puts name.upcase    # RUBY
puts name           # Ruby

Calling the same methods followed by an exclamation mark will both return lowercase/uppercase version of the string and will also change the content of the variable. 

puts name.downcase! # ruby
puts name           # ruby

puts name.upcase!   # RUBY
puts name           # RUBY

Full example

examples/ruby/case.rb


name = 'Foo'
puts name           # Ruby
puts name.downcase  # ruby
puts name.upcase    # RUBY
puts name           # Ruby


puts name.downcase! # ruby
puts name           # ruby

puts name.upcase!   # RUBY
puts name           # RUBY