Replacing backreferences in Regular Expressions with its matched content.

replacing.rb

require 'pp'
text  = 'and the day is 08/11/1993 of course'
regex = 'the (day) (.+) <date> of'
result = regex.dup

until (s ||= 0) >= result.length
  break unless section = (/(\((?!\?)(?:[^\(]+?[^\\]\)))/).match(result, s)
  matches = Regexp.new(result.gsub(/<.+?>/, '.+?')).match(text)
  
  offset = section.offset(0)
  section = section[0]

  result = result[0..offset.first - 1] + matches[1] + result[offset.last..result.length]
  s = 0
end

puts "text: #{text}"      # text:   and the day is 08/11/1993 of course
puts "regex: #{regex}"    # regex:  the (day) (.+) <date> of
puts "result: #{result}"  # result: the day is <date> of

The idea of this is to create a template system for regular expressions.
We have the regular expression the (day) (.+) <date> of and we want to execute it against and the day is 08/11/1993 of course, we want it to ignore the 08/11/1993 part and then we want to get a modified version of the regular expression that contains the matched content of the regular expression: the day is <date> of.