diff --git a/tool/generic_erb.rb b/tool/generic_erb.rb
index 6af995fc13..47bffd830c 100644
--- a/tool/generic_erb.rb
+++ b/tool/generic_erb.rb
@@ -5,31 +5,23 @@
 
 require 'erb'
 require 'optparse'
-require_relative 'lib/vpath'
-require_relative 'lib/colorize'
+require_relative 'lib/output'
 
-vpath = VPath.new
-timestamp = nil
-output = nil
-ifchange = nil
+out = Output.new
 source = false
-color = nil
 templates = []
 
 ARGV.options do |o|
-  o.on('-t', '--timestamp[=PATH]') {|v| timestamp = v || true}
   o.on('-i', '--input=PATH') {|v| template << v}
-  o.on('-o', '--output=PATH') {|v| output = v}
-  o.on('-c', '--[no-]if-change') {|v| ifchange = v}
   o.on('-x', '--source') {source = true}
-  o.on('--color') {color = true}
-  vpath.def_options(o)
+  out.def_options(o)
   o.order!(ARGV)
   templates << (ARGV.shift or abort o.to_s) if templates.empty?
 end
-color = Colorize.new(color)
-unchanged = color.pass("unchanged")
-updated = color.fail("updated")
+
+# Used in prelude.c.tmpl and unicode_norm_gen.tmpl
+output = out.path
+vpath = out.vpath
 
 result = templates.map do |template|
   if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
@@ -41,21 +33,4 @@ result = templates.map do |template|
   source ? erb.src : proc{erb.result(binding)}.call
 end
 result = result.size == 1 ? result[0] : result.join("")
-if output
-  if ifchange and (vpath.open(output, "rb") {|f| f.read} rescue nil) == result
-    puts "#{output} #{unchanged}"
-  else
-    open(output, "wb") {|f| f.print result}
-    puts "#{output} #{updated}"
-  end
-  if timestamp
-    if timestamp == true
-      dir, base = File.split(output)
-      timestamp = File.join(dir, ".time." + base)
-    end
-    File.open(timestamp, 'a') {}
-    File.utime(nil, nil, timestamp)
-  end
-else
-  print result
-end
+out.write(result)
diff --git a/tool/lib/output.rb b/tool/lib/output.rb
new file mode 100644
index 0000000000..5e0e878322
--- /dev/null
+++ b/tool/lib/output.rb
@@ -0,0 +1,47 @@
+require_relative 'vpath'
+require_relative 'colorize'
+
+class Output
+  attr_reader :path, :vpath
+
+  def initialize
+    @path = @timestamp = @ifchange = @color = nil
+    @vpath = VPath.new
+  end
+
+  def def_options(opt)
+    opt.on('-o', '--output=PATH') {|v| @path = v}
+    opt.on('-t', '--timestamp[=PATH]') {|v| @timestamp = v || true}
+    opt.on('-c', '--[no-]if-change') {|v| @ifchange = v}
+    opt.on('--color') {@color = true}
+    @vpath.def_options(opt)
+  end
+
+  def write(data)
+    unless @path
+      $stdout.print data
+      return true
+    end
+    color = Colorize.new(@color)
+    unchanged = color.pass("unchanged")
+    updated = color.fail("updated")
+
+    if @ifchange and (@vpath.read(@path, "rb") == data rescue false)
+      puts "#{@path} #{unchanged}"
+      written = false
+    else
+      File.binwrite(@path, data)
+      puts "#{@path} #{updated}"
+      written = true
+    end
+    if timestamp = @timestamp
+      if timestamp == true
+        dir, base = File.split(@path)
+        timestamp = File.join(dir, ".time." + base)
+      end
+      File.binwrite(timestamp, '')
+      File.utime(nil, nil, timestamp)
+    end
+    written
+  end
+end