does a join on 2 files based on 1st capture of regex. e.g.: join-on Gemfile "gem '([^']*)'" Gemfile.lock " *([^ ]*)"

join-on

#!/usr/bin/env ruby
# example use: join-on Gemfile "gem '([^']*)'" Gemfile.lock " *([^ ]*)"
file1, cap1, file2, cap2 = *ARGV

r1 = Regexp.new(cap1)
r2 = Regexp.new(cap2)
line_match_number = []
n = 0
max_len = 0
File.open(file1).each do |line|
  match = r1.match(line)
  n+=1
  if match
    line_match_number << [line, match[1], n]
    max_len = [max_len, line.length].max
  end
end
p1 = Math.log10(line_match_number.last[2]).to_i + 1

match_to_line_number = {}
n=0
File.open(file2).each do |line|
  match = r2.match(line)
  n+=1
    if match
      match_to_line_number[match[1]] = [line, n]
  end
end
p2 = Math.log10(n).to_i + 1
line_match_number.each do |line, match, number|
  if ln = match_to_line_number[match]
    puts "#{number.to_s.rjust(p1)}|#{line[0...-1].ljust(max_len)}|#{ln[1].to_s.rjust(p2)}|#{ln[0]}"
  else
    puts "#{number.to_s.rjust(p1)}|#{line[0...-1].ljust(max_len)}|"
  end
end