diff --git a/tool/file2lastrev.rb b/tool/file2lastrev.rb
index 90816ae83e..8ead4961e7 100755
--- a/tool/file2lastrev.rb
+++ b/tool/file2lastrev.rb
@@ -1,110 +1,10 @@
 #!/usr/bin/env ruby
 
-ENV.delete('PWD')
-
 require 'optparse'
-
-unless File.respond_to? :realpath
-  require 'pathname'
-  def File.realpath(arg)
-    Pathname(arg).realpath.to_s
-  end
-end
+require File.expand_path('../vcs', __FILE__)
 
 Program = $0
 
-class VCS
-  class NotFoundError < RuntimeError; end
-
-  @@dirs = []
-  def self.register(dir)
-    @@dirs << [dir, self]
-  end
-
-  def self.detect(path)
-    @@dirs.each do |dir, klass|
-      return klass.new(path) if File.directory?(File.join(path, dir))
-      prev = path
-      loop {
-        curr = File.realpath(File.join(prev, '..'))
-        break if curr == prev	# stop at the root directory
-        return klass.new(path) if File.directory?(File.join(curr, dir))
-        prev = curr
-      }
-    end
-    raise VCS::NotFoundError, "does not seem to be under a vcs: #{path}"
-  end
-
-  def initialize(path)
-    @srcdir = path
-    super()
-  end
-
-  # return a pair of strings, the last revision and the last revision in which
-  # +path+ was modified.
-  def get_revisions(path)
-    path = relative_to(path)
-    last, changed, *rest = Dir.chdir(@srcdir) {self.class.get_revisions(path)}
-    last or raise "last revision not found"
-    changed or raise "changed revision not found"
-    return last, changed, *rest
-  end
-
-  def relative_to(path)
-    if path
-      srcdir = File.realpath(@srcdir)
-      path = File.realpath(path)
-      list1 = srcdir.split(%r{/})
-      list2 = path.split(%r{/})
-      while !list1.empty? && !list2.empty? && list1.first == list2.first
-        list1.shift
-        list2.shift
-      end
-      if list1.empty? && list2.empty?
-        "."
-      else
-        ([".."] * list1.length + list2).join("/")
-      end
-    else
-      '.'
-    end
-  end
-
-  class SVN < self
-    register(".svn")
-
-    def self.get_revisions(path)
-      begin
-        nulldevice = %w[/dev/null NUL NIL: NL:].find {|dev| File.exist?(dev)}
-        if nulldevice
-          save_stderr = STDERR.dup
-          STDERR.reopen nulldevice, 'w'
-        end
-        info_xml = `svn info --xml "#{path}"`
-      ensure
-        if save_stderr
-          STDERR.reopen save_stderr
-          save_stderr.close
-        end
-      end
-      _, last, _, changed, _ = info_xml.split(/revision="(\d+)"/)
-      [last, changed]
-    end
-  end
-
-  class GIT < self
-    register(".git")
-
-    def self.get_revisions(path)
-      logcmd = %Q[git log -n1 --grep="^ *git-svn-id: .*@[0-9][0-9]* "]
-      idpat = /git-svn-id: .*?@(\d+) \S+\Z/
-      last = `#{logcmd}`[idpat, 1]
-      changed = path ? `#{logcmd} "#{path}"`[idpat, 1] : last
-      [last, changed]
-    end
-  end
-end
-
 @output = nil
 def self.output=(output)
   if @output and @output != output
diff --git a/tool/vcs.rb b/tool/vcs.rb
new file mode 100644
index 0000000000..e7cb610767
--- /dev/null
+++ b/tool/vcs.rb
@@ -0,0 +1,102 @@
+# vcs
+
+ENV.delete('PWD')
+
+unless File.respond_to? :realpath
+  require 'pathname'
+  def File.realpath(arg)
+    Pathname(arg).realpath.to_s
+  end
+end
+
+class VCS
+  class NotFoundError < RuntimeError; end
+
+  @@dirs = []
+  def self.register(dir)
+    @@dirs << [dir, self]
+  end
+
+  def self.detect(path)
+    @@dirs.each do |dir, klass|
+      return klass.new(path) if File.directory?(File.join(path, dir))
+      prev = path
+      loop {
+        curr = File.realpath(File.join(prev, '..'))
+        break if curr == prev	# stop at the root directory
+        return klass.new(path) if File.directory?(File.join(curr, dir))
+        prev = curr
+      }
+    end
+    raise VCS::NotFoundError, "does not seem to be under a vcs: #{path}"
+  end
+
+  def initialize(path)
+    @srcdir = path
+    super()
+  end
+
+  # return a pair of strings, the last revision and the last revision in which
+  # +path+ was modified.
+  def get_revisions(path)
+    path = relative_to(path)
+    last, changed, *rest = Dir.chdir(@srcdir) {self.class.get_revisions(path)}
+    last or raise "last revision not found"
+    changed or raise "changed revision not found"
+    return last, changed, *rest
+  end
+
+  def relative_to(path)
+    if path
+      srcdir = File.realpath(@srcdir)
+      path = File.realpath(path)
+      list1 = srcdir.split(%r{/})
+      list2 = path.split(%r{/})
+      while !list1.empty? && !list2.empty? && list1.first == list2.first
+        list1.shift
+        list2.shift
+      end
+      if list1.empty? && list2.empty?
+        "."
+      else
+        ([".."] * list1.length + list2).join("/")
+      end
+    else
+      '.'
+    end
+  end
+
+  class SVN < self
+    register(".svn")
+
+    def self.get_revisions(path)
+      begin
+        nulldevice = %w[/dev/null NUL NIL: NL:].find {|dev| File.exist?(dev)}
+        if nulldevice
+          save_stderr = STDERR.dup
+          STDERR.reopen nulldevice, 'w'
+        end
+        info_xml = `svn info --xml "#{path}"`
+      ensure
+        if save_stderr
+          STDERR.reopen save_stderr
+          save_stderr.close
+        end
+      end
+      _, last, _, changed, _ = info_xml.split(/revision="(\d+)"/)
+      [last, changed]
+    end
+  end
+
+  class GIT < self
+    register(".git")
+
+    def self.get_revisions(path)
+      logcmd = %Q[git log -n1 --grep="^ *git-svn-id: .*@[0-9][0-9]* "]
+      idpat = /git-svn-id: .*?@(\d+) \S+\Z/
+      last = `#{logcmd}`[idpat, 1]
+      changed = path ? `#{logcmd} "#{path}"`[idpat, 1] : last
+      [last, changed]
+    end
+  end
+end