gistfile1.rb

class Wildcards < Struct.new(:hash, :definitions)
  def replace(a = hash, b = definitions)
    a.merge(b) do |_, left, right|
      if left.is_a? Hash
        compare(left, right)
      else
        left == '*' ? right : left
      end
    end
  end
  
  # or if you want to codegolf it...
  def replace(a = hash, b = definitions)
    a.merge(b){|_,l,r|l.is_a?(Hash)?replace(l,r):l=='*'?r:l}
  end
end

Wildcards.new(
  {:foo=>"*", :bar=>{:baz=>"*", :buck=>"buck"}},
  {:foo=>"bar", :bar=>{:baz=>"baz", :buck=>"buck"}}
).replace

# or...

module WildcardParser
  def self.replace(a, b)
    a.merge(b){|_,l,r|l.is_a?(Hash)?replace(l,r):l=='*'?r:l}
  end
end

WildcardParser::replace({:foo=>"*", :bar=>{:baz=>"*", :buck=>"buck"}}, {:foo=>"bar", :bar=>{:baz=>"baz", :buck=>"buck"}})