Upcase, downcase

The upcase() and downcase() methods affect letters. Upcase changes lowercase letters to uppercase. And downcase changes uppercase letters to lowercase.

You must assign to the result of upcase() and downcase(). The original string instance is not modified—a modified copy of the string is made.

First example

We begin by calling the upcase method, and then invoking the downcase method on the result. When we call these methods, only letters are affected.

# An input string.
value = "BLUE bird"

# Change cases.
upper = value.upcase()
lower = value.downcase()

# Display results.
puts upper
puts lower
BLUE BIRD
blue bird

In-place

Suppose we want to modify a string in-place, without having to assign the result of upcase or downcase. We can use an exclamation mark to modify the current string variable.

test = "bird"

# Use exclamation mark to modify the string in-place.
test.upcase!
puts test
BIRD

In Ruby, we sometimes have logic that preprocesses files containing data that may have inconsistent cases. Often we want to lowercase (or uppercase) every string we encounter.