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

Question

%w[ ]   Non-interpolated Array of words, separated by whitespace %W[ ]   Interpolated Array of words, separated by whitespace 

Usage:

p %w{one one two three 0 1 1 2 3} # = > ["one", "one", "two", "three", "0", "1", "1", "2", "3"] p %W{one one two three 0 1 1 2 3} # = > ["one", "one", "two", "three", "0", "1", "1", "2", "3"] p %w{C:\ C:\Windows} # => ["C: C:\\Windows"] p %W{C:\ C:\Windows} # => ["C: C:Windows"] 

My question is... what's the difference?

Answer 1

%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"] 

Answer 2

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.