gsub_benchmark.rb

require 'benchmark'

PATTERN = /@@@(.*?)@@@/
TIMES = 1_000

string = 'one @@@two@@@ three' * 1000

Benchmark.bm(10) do |benchmark|
  benchmark.report('global') do
    TIMES.times do
      string.gsub(PATTERN) { Regexp.last_match(1).reverse }
    end
  end
  benchmark.report('local') do
    TIMES.times do
      string.gsub(PATTERN) { |match| PATTERN.match(match)[1].reverse }
    end
  end
end

output

                user     system      total        real
global      2.530000   0.000000   2.530000 (  2.604000)
local       4.150000   0.020000   4.170000 (  4.225362)