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  • erb.rb

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The optional filename argument passed to Kernel#eval when the ERB code is run


The Ruby code generated by ERB

Public Class Methods

new(str, safe_level=nil, trim_mode=nil, eoutvar='_erbout') click to toggle source

Constructs a new ERB object with the template specified in str.

An ERB object works by building a chunk of Ruby code that will output the completed template when run. If safe_level is set to a non-nil value, ERB code will be run in a separate thread with $SAFE set to the provided level.

If trim_mode is passed a String containing one or more of the following modifiers, ERB will adjust its code generation as listed:

%  enables Ruby code processing for lines beginning with %
<> omit newline for lines starting with <% and ending in %>
>  omit newline for lines ending in %>
-  omit blank lines ending in -%>

eoutvar can be used to set the name of the variable ERB will build up its output in. This is useful when you need to run multiple ERB templates through the same binding and/or when you want to control where output ends up. Pass the name of the variable to be used inside a String.


require "erb"

# build data class
class Listings
  PRODUCT = { :name => "Chicken Fried Steak",
              :desc => "A well messages pattie, breaded and fried.",
              :cost => 9.95 }

  attr_reader :product, :price

  def initialize( product = "", price = "" )
    @product = product
    @price = price

  def build
    b = binding
    # create and run templates, filling member data variables"      <%= PRODUCT[:name] %>
      <%= PRODUCT[:desc] %>
".gsub(/^\s+/, ""), 0, "", "@product").result b"      <%= PRODUCT[:name] %> -- <%= PRODUCT[:cost] %>
      <%= PRODUCT[:desc] %>
".gsub(/^\s+/, ""), 0, "", "@price").result b

# setup template data
listings =

puts listings.product + "\n" + listings.price


Chicken Fried Steak
A well messages pattie, breaded and fried.

Chicken Fried Steak -- 9.95
A well messages pattie, breaded and fried.
               # File erb.rb, line 795
def initialize(str, safe_level=nil, trim_mode=nil, eoutvar='_erbout')
  @safe_level = safe_level
  compiler = make_compiler(trim_mode)
  set_eoutvar(compiler, eoutvar)
  @src, @enc = *compiler.compile(str)
  @filename = nil
version() click to toggle source

Returns revision information for the erb.rb module.

               # File erb.rb, line 263
def self.version
  "erb.rb [2.1.0 #{ERB::Revision.split[1]}]"

Public Instance Methods

def_class(superklass=Object, methodname='result') click to toggle source

Define unnamed class which has methodname as instance method, and return it.


class MyClass_
  def initialize(arg1, arg2)
    @arg1 = arg1;  @arg2 = arg2
filename = 'example.rhtml'  # @arg1 and @arg2 are used in example.rhtml
erb =
erb.filename = filename
MyClass = erb.def_class(MyClass_, 'render()')
print'foo', 123).render()
               # File erb.rb, line 906
def def_class(superklass=Object, methodname='result')
  cls =
  def_method(cls, methodname, @filename || '(ERB)')
def_method(mod, methodname, fname='(ERB)') click to toggle source

Define methodname as instance method of mod from compiled Ruby source.


filename = 'example.rhtml'   # 'arg1' and 'arg2' are used in example.rhtml
erb =
erb.def_method(MyClass, 'render(arg1, arg2)', filename)
print'foo', 123)
               # File erb.rb, line 869
def def_method(mod, methodname, fname='(ERB)')
  src = self.src
  magic_comment = "#coding:#{@enc}\n"
  mod.module_eval do
    eval(magic_comment + "def #{methodname}\n" + src + "\nend\n", binding, fname, -2)
def_module(methodname='erb') click to toggle source

Create unnamed module, define methodname as instance method of it, and return it.


filename = 'example.rhtml'   # 'arg1' and 'arg2' are used in example.rhtml
erb =
erb.filename = filename
MyModule = erb.def_module('render(arg1, arg2)')
class MyClass
  include MyModule
               # File erb.rb, line 887
def def_module(methodname='erb')
  mod =
  def_method(mod, methodname, @filename || '(ERB)')
make_compiler(trim_mode) click to toggle source

Creates a new compiler for ERB. See for details

               # File erb.rb, line 806
def make_compiler(trim_mode)
result(b=new_toplevel) click to toggle source

Executes the generated ERB code to produce a completed template, returning the results of that code. (See ::new for details on how this process can be affected by safe_level.)

b accepts a Binding or Proc object which is used to set the context of code evaluation.

               # File erb.rb, line 842
def result(b=new_toplevel)
  if @safe_level
    proc {
      $SAFE = @safe_level
      eval(@src, b, (@filename || '(erb)'), 0)
    eval(@src, b, (@filename || '(erb)'), 0)
run(b=new_toplevel) click to toggle source

Generate results and print them. (see #result)

               # File erb.rb, line 830
def run(b=new_toplevel)
  print self.result(b)
set_eoutvar(compiler, eoutvar = '_erbout') click to toggle source

Can be used to set eoutvar as described in ::new. It’s probably easier to just use the constructor though, since calling this method requires the setup of an ERB compiler object.

               # File erb.rb, line 822
def set_eoutvar(compiler, eoutvar = '_erbout')
  compiler.put_cmd = "#{eoutvar}.concat"
  compiler.insert_cmd = "#{eoutvar}.concat"
  compiler.pre_cmd = ["#{eoutvar} = ''"]
  compiler.post_cmd = ["#{eoutvar}.force_encoding(__ENCODING__)"]