rubyの%記法にハマった ref: https://qiita.com/kyohei_shimada/items/07e4db87a2e01af33d1d

file3.txt

require 'active_support'
require 'active_support/core_ext/hash/slice'

# キーを２つ指定したつもりが単なる文字列になってしまっていた．．．
{ 'key1' => 'hoge', 'key2' => 'fuga', 'key3' => 'piyo' }.slice(*" key1 key2 ")
#=> { }

file5.txt

This is a pen!

sample1.rb

require 'active_support'
require 'active_support/core_ext/hash/slice'

{ 'key1' => 'hoge', 'key2' => 'fuga', 'key3' => 'piyo' }.slice(*%w( key1 key2 ))
#=> { "key1" => "hoge", "key2" => "fuga" }

sample2.rb

require 'active_support'
require 'active_support/core_ext/hash/slice'

{ 'key1' => 'hoge', 'key2' => 'fuga', 'key3' => 'piyo' }.slice(%( key1 key2 ))
#=> { }

sample3.rb

%w( a b c ) #=> ["a", "b", "c"]
%( a b c ) #=> " a b c "

sample4.rb

x = %
This is a pen!

puts x