What is the difference between %w{} and %W{} upper and lower case percent W array literals in Ruby?

%W treats the strings as double quoted whereas %w treats them as single quoted (and therefore won’t interpolate expressions or numerous escape sequences). Try your arrays again with ruby expressions and you'll see a difference.

EXAMPLE:

myvar = 'one'
p %w{#{myvar} two three 1 2 3} # => ["\#{myvar}", "two", "three", "1", "2", "3"]
p %W{#{myvar} two three 1 2 3} # => ["one", "two", "three", "1", "2", "3"]

Let's skip the array confusion and talk about interpolation versus none:

irb(main):001:0> [ 'foo\nbar', "foo\nbar" ]
=> ["foo\\nbar", "foo\nbar"]
irb(main):002:0> [ 'foo\wbar', "foo\wbar" ]
=> ["foo\\wbar", "foowbar"]

The difference in behavior is consistent with how single-quoted versus double-quoted strings behave.