regexptune.rb

a = /\Aforward(?![^\.]).*\Z/
b = /\Aforward[^\.].*\Z/
n = 1000000
require 'benchmark'

Benchmark.bm {|x|
  x.report("a") do
    n.times do
      a =~ "forward.test"
    end
  end

  x.report("b") do
    n.times do
      b =~ "forward.test"
    end
  end
}