Benchmark of Ruby long string concatenation mechanisms, based on http://blog.codahale.com/2006/04/18/ever-wonder-which-is-the-fastest-way-to-concatenate-strings-in-ruby/

benchmark_stringcat.rb

require 'benchmark'

NUM_TRIALS = 10_000_000

Benchmark.bm(20) do |x|
  x.report('no concatenation') do
    NUM_TRIALS.times do
      y = "onetwothree"
    end
  end
  x.report('+') do
    NUM_TRIALS.times do
      y = 'one' +
          'two' +
          'three'
    end
  end
  x.report('\\') do
    NUM_TRIALS.times do
      y = 'one' \
          'two' \
          'three'
    end
  end
  x.report('<<') do
    NUM_TRIALS.times do
      y = 'one' <<
          'two' <<
          'three'
    end
  end
end

results

$ ruby benchmark_stringcat.rb 
                          user     system      total        real
no concatenation      1.320000   0.010000   1.330000 (  1.332485)
+                     5.690000   0.000000   5.690000 (  5.697842)
\                     1.380000   0.000000   1.380000 (  1.387014)
<<                    5.340000   0.000000   5.340000 (  5.348465)