What does %w(array) mean?

Solution 1:

%w(foo bar) is a shortcut for ["foo", "bar"]. Meaning it's a notation to write an array of strings separated by spaces instead of commas and without quotes around them. You can find a list of ways of writing literals in zenspider's quickref.

Solution 2:

I think of %w() as a "word array" - the elements are delimited by spaces and it returns an array of strings.

Here are all % literals:

%w() array of strings
%r() regular expression.
%q() string
%x() a shell command (returning the output string)
%i() array of symbols (Ruby >= 2.0.0)
%s() symbol
%() (without letter) shortcut for %Q()

The delimiters ( and ) can be replaced with a lot of variations, like [ and ], |, !, etc.

When using a capital letter %W() you can use string interpolation #{variable}, similar to the " and ' string delimiters. This rule works for all the other % literals as well.

abc = 'a b c'
%w[1 2#{abc} d] #=> ["1", "2\#{abc}", "d"]
%W[1 2#{abc} d] #=> ["1", "2a b c", "d"]

Solution 3:

There is also %s that allows you to create any symbols, for example:

%s|some words|          #Same as :'some words'
%s[other words]         #Same as :'other words'
%s_last example_        #Same as :'last example'

Since Ruby 2.0.0 you also have:

%i( a b c )   # => [ :a, :b, :c ]
%i[ a b c ]   # => [ :a, :b, :c ]
%i_ a b c _   # => [ :a, :b, :c ]
# etc...

Solution 4:

%W and %w allow you to create an Array of strings without using quotes and commas.

Solution 5:

Though it's an old post, the question keep coming up and the answers don't always seem clear to me, so, here's my thoughts:

%w and %W are examples of General Delimited Input types, that relate to Arrays. There are other types that include %q, %Q, %r, %x and %i.

The difference between the upper and lower case version is that it gives us access to the features of single and double quotes. With single quotes and (lowercase) %w, we have no code interpolation (#{someCode}) and a limited range of escape characters that work (\\, \n). With double quotes and (uppercase) %W we do have access to these features.

The delimiter used can be any character, not just the open parenthesis. Play with the examples above to see that in effect.

For a full write up with examples of %w and the full list, escape characters and delimiters, have a look at "Ruby - %w vs %W – secrets revealed!"