Using Ruby 1.9.3, Rails 3.2, I have the following:
\"every good boy does fine\".gsub(\"every\", \"all\").gsub(\"boy\", \"girl\").gsub(\"fine\", \"well\")
# =
String#gsub and Hash#fetch will be the good choice for this.
a = "every good boy does fine"
h = {"every" => "all","boy" => "girl", "fine" =>"well" }
a.gsub(/\w+/) { |m| h.fetch(m,m)}
# => "all good girl does well"
or,
a = "every good boy does fine"
h = {"every" => "all","boy" => "girl", "fine" =>"well" }
Regexp.new("^#{h.keys.join('|')}$") # => /^every|boy|fine$/
a.gsub(Regexp.new("^#{h.keys.join('|')}$"),h)
# => "all good girl does well"