diff --git a/tool/merger.rb b/tool/merger.rb
new file mode 100755
index 0000000000..48fddc38f2
--- /dev/null
+++ b/tool/merger.rb
@@ -0,0 +1,207 @@
+#! /bin/ruby
+# This needs ruby 1.9 and subversion.
+# run this in a repository to commit.
+
+require 'date'
+require 'tempfile'
+
+$repos = 'svn+ssh://svn@ci.ruby-lang.org/ruby/'
+ENV['LC_ALL'] = 'C'
+
+def help
+  puts <<-end
+simple backport
+  ruby #$0 1234
+
+range backport
+  ruby #$0 1234:5678
+
+backport from other branch
+  ruby #$0 17502 mvm
+
+revision increment
+  ruby #$0 revisionup
+
+tagging
+  ruby #$0 tag
+
+* all operations shall be applied to the working directory.
+end
+end
+
+def version
+  v = p = nil
+  open 'version.h', 'rb' do |f|
+    f.each_line do |l|
+      case l
+      when /^#define RUBY_VERSION "(\d)\.(\d)\.(\d)"$/
+        v = $~.captures
+      when /^#define RUBY_PATCHLEVEL (-?\d+)$/
+        p = $1
+      end
+    end
+  end
+  return v, p
+end
+
+def interactive str
+  loop do
+    yield
+    STDERR.puts str
+    case STDIN.gets
+    when /\Aa/i then exit
+    when /\Ar/i then redo
+    when /\Ay/i then break
+    else exit
+    end
+  end
+end
+
+def version_up
+  d = Date.today
+  system *%w'svn revert version.h'
+  v, p = version
+
+  teeny = v[2]
+  case v
+  when %w/1 9 2/
+    teeny = 1
+  end
+
+  p = p.to_i
+  if p != -1
+    p += 1
+  end
+
+  str = open 'version.h', 'rb' do |f| f.read end
+  [%W[RUBY_VERSION      "#{v.join '.'}"],
+   %W[RUBY_VERSION_CODE  #{v.join ''}],
+   %W[RUBY_VERSION_MAJOR #{v[0]}],
+   %W[RUBY_VERSION_MINOR #{v[1]}],
+   %W[RUBY_VERSION_TEENY #{teeny}],
+   %W[RUBY_RELEASE_DATE "#{d.strftime '%Y-%m-%d'}"],
+   %W[RUBY_RELEASE_CODE  #{d.strftime '%Y%m%d'}],
+   %W[RUBY_PATCHLEVEL    #{p}],
+   %W[RUBY_RELEASE_YEAR  #{d.year}],
+   %W[RUBY_RELEASE_MONTH #{d.month}],
+   %W[RUBY_RELEASE_DAY   #{d.day}],
+  ].each do |(k, i)|
+    str.sub! /^(#define\s+#{k}\s+).*$/, "\\1#{i}"
+  end
+  str.sub! /\s+\z/m, ''
+  fn = sprintf 'version.h.tmp.%032b', rand(1 << 31)
+  File.rename 'version.h', fn
+  open 'version.h', 'wb' do |f|
+    f.puts str
+  end
+  File.unlink fn
+end
+
+def tag intv_p = false
+  v, p = version
+  x = v.join('_')
+  y = $repos + 'branches/ruby_' + x
+  z = 'v' + x + '_' + p
+  w = $repos + 'tags/' + z
+  if intv_p
+    interactive "OK? svn cp -m \"add tag #{z}\" #{y} #{w} ([y]es|[a]bort|[r]etry)" do
+    end
+  end
+  system *%w'svn cp -m' + ["add tag #{z}"] + [y, w]
+end
+
+def default_merge_branch
+  /branches\/ruby_1_8_/ =~ IO.binread(".svn/entries", 100) ? 'branches/ruby_1_8' : 'trunk'
+end
+
+case ARGV[0]
+when "up", /\A(ver|version|rev|revision|lv|level|patch\s*level)\s*up/
+  version_up
+  system 'svn diff version.h'
+when "tag"
+  tag :interactive
+when nil, "-h", "--help"
+  help
+  exit
+else
+  q = $repos + (ARGV[1] || default_merge_branch)
+  revs = ARGV[0].split /,\s*/
+  log = ''
+  log_svn = ''
+
+  revs.each do |rev|
+    case rev
+    when /\A\d+:\d+\z/
+      r = ['-r', rev]
+    when /\A\d+\z/
+      r = ['-c', rev]
+    when nil then
+      puts "#$0 revision"
+      exit
+    end
+
+    l = IO.popen %w'svn diff' + r + %w'--diff-cmd=diff -x -pU0' + [File.join(q, 'ChangeLog')] do |f|
+      f.read
+    end
+
+    log << l
+    log_svn << l.lines.grep(/^\+\t/).join.gsub(/^\+/, '').gsub(/^\t\*/, "\n\t\*")
+
+    if log_svn.empty?
+      log_svn = IO.popen %w'svn log ' + r + [q] do |f|
+        f.read
+      end
+    end
+
+    a = %w'svn merge --accept=postpone' + r + [q]
+    STDERR.puts a.join(' ')
+
+    system(*a)
+    system *%w'svn revert ChangeLog' if /^\+/ =~ l
+  end
+
+  if /^\+/ =~ log
+    system *%w'svn revert ChangeLog'
+    IO.popen %w'patch -p0', 'wb' do |f|
+      f.write log.gsub(/\+(Mon|Tue|Wed|Thu|Fri|Sat|Sun) (Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) [ 123][0-9] [012][0-9]:[0-5][0-9]:[0-5][0-9] \d\d\d\d/,
+                       # this format-time-string was from the file local variables of ChangeLog
+                       '+'+Time.now.strftime('%a %b %e %H:%M:%S %Y'))
+    end
+    system *%w'touch ChangeLog' # needed somehow, don't know why...
+  else
+    STDERR.puts '*** You should write ChangeLog NOW!!! ***'
+  end
+
+  version_up
+  f = Tempfile.new 'merger.rb'
+  f.printf "merge revision(s) %s:\n", ARGV[0]
+  f.write log_svn
+  f.flush
+  f.close
+  f.open # avoid gc
+
+  interactive 'conflicts resolved? (y:yes, a:abort, r:retry, otherwise abort)' do
+    f.rewind
+    IO.popen('-', 'wb') do |g|
+      if g
+        g << `svn stat`
+        g << "\n\n"
+        g << f.read
+        g << "\n\n"
+        g << `svn diff --diff-cmd=diff -x -upw`
+      else
+        exec 'less'
+      end
+    end
+    Process.waitall
+  end
+
+  if system *%w'svn ci -F' + [f.path]
+    # tag :interactive # no longer needed.
+    system 'rm -f subversion.commitlog'
+  else
+    puts 'commit failed; try again.'
+  end
+
+  f.close
+end