Measure efficiency of several methods of string concatenation.

result.txt

                              user     system      total        real
Array#push and join       0.360000   0.040000   0.400000 (  0.398396)
String#concat 1           0.240000   0.030000   0.270000 (  0.267289)
String#concat 2           0.260000   0.040000   0.300000 (  0.297610)
Array#join with a const   0.090000   0.030000   0.120000 (  0.121947)
String#concat with const  0.100000   0.030000   0.130000 (  0.134064)

str-join.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-
$VERBOSE = true
=begin
Measure efficiency of several methods of string concatenation.
=end

require 'benchmark'

STR_TO_ADD = ["a", "b"].join("\t") + "\n"
NUM_TRIAL = 100000
Benchmark.bm( 24 ){|bm|
  bm.report( 'Array#push and join' ){
    a = []
    NUM_TRIAL.times do
      a << (["a", "b"].join("\t"))
    end
    s = a.join("\n")
    s << "\n"
  }
  bm.report( 'String#concat 1' ){
    s = ""
    NUM_TRIAL.times do
      s << "a" << "\t" << "b" << "\n"
    end
  }
  bm.report( 'String#concat 2' ){
    s = ""
    NUM_TRIAL.times do
      s << (["a", "b"].join("\t"))
    end
  }
  bm.report( 'Array#join with a const' ){
    a = []
    NUM_TRIAL.times do
      a << STR_TO_ADD
    end
    s = a.join ''
  }
  bm.report( 'String#concat with const' ){
    s = ""
    NUM_TRIAL.times do
      s << STR_TO_ADD
    end
  }
}