ERB

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.

Example¶ ↑

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
  end

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

# setup template data
listings = Listings.new
listings.build

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

Generates

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 813
def initialize(str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eoutvar=NOT_GIVEN, trim_mode: nil, eoutvar: '_erbout')
  # Complex initializer for $SAFE deprecation at Feature #14256, which should be removed at Ruby 2.7.
  if safe_level != NOT_GIVEN
    warn 'Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.', uplevel: 1 if $VERBOSE
  else
    safe_level = nil
  end
  if legacy_trim_mode != NOT_GIVEN
    warn 'Passing trim_mode with the 3rd argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, trim_mode: ...) instead.', uplevel: 1 if $VERBOSE
    trim_mode = legacy_trim_mode
  end
  if legacy_eoutvar != NOT_GIVEN
    warn 'Passing eoutvar with the 4th argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, eoutvar: ...) instead.', uplevel: 1 if $VERBOSE
    eoutvar = legacy_eoutvar
  end

  @safe_level = safe_level
  compiler = make_compiler(trim_mode)
  set_eoutvar(compiler, eoutvar)
  @src, @encoding, @frozen_string = *compiler.compile(str)
  @filename = nil
  @lineno = 0
end
            

Returns revision information for the erb.rb module.

 
               # File erb.rb, line 264
def self.version
  "erb.rb [2.2.0 #{ERB::Revision.split[1]}]"
end
            

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

example:

class MyClass_
  def initialize(arg1, arg2)
    @arg1 = arg1;  @arg2 = arg2
  end
end
filename = 'example.rhtml'  # @arg1 and @arg2 are used in example.rhtml
erb = ERB.new(File.read(filename))
erb.filename = filename
MyClass = erb.def_class(MyClass_, 'render()')
print MyClass.new('foo', 123).render()

 
               # File erb.rb, line 973
def def_class(superklass=Object, methodname='result')
  cls = Class.new(superklass)
  def_method(cls, methodname, @filename || '(ERB)')
  cls
end
            

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

example:

filename = 'example.rhtml'   # 'arg1' and 'arg2' are used in example.rhtml
erb = ERB.new(File.read(filename))
erb.def_method(MyClass, 'render(arg1, arg2)', filename)
print MyClass.new.render('foo', 123)

 
               # File erb.rb, line 937
def def_method(mod, methodname, fname='(ERB)')
  src = self.src.sub(/^(?!#|$)/) {"def #{methodname}\n"} << "\nend\n"
  mod.module_eval do
    eval(src, binding, fname, -1)
  end
end
            

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

example:

filename = 'example.rhtml'   # 'arg1' and 'arg2' are used in example.rhtml
erb = ERB.new(File.read(filename))
erb.filename = filename
MyModule = erb.def_module('render(arg1, arg2)')
class MyClass
  include MyModule
end

 
               # File erb.rb, line 954
def def_module(methodname='erb')
  mod = Module.new
  def_method(mod, methodname, @filename || '(ERB)')
  mod
end
            

Creates a new compiler for ERB. See ERB::Compiler.new for details

 
               # File erb.rb, line 842
def make_compiler(trim_mode)
  ERB::Compiler.new(trim_mode)
end
            

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 object which is used to set the context of code evaluation.

 
               # File erb.rb, line 890
def result(b=new_toplevel)
  if @safe_level
    proc do
      prev_safe_level = $SAFE
      $SAFE = @safe_level
      eval(@src, b, (@filename || '(erb)'), @lineno)
    ensure
      $SAFE = prev_safe_level
    end.call
  else
    eval(@src, b, (@filename || '(erb)'), @lineno)
  end
end
            

Render a template on a new toplevel binding with local variables specified by a Hash object.

 
               # File erb.rb, line 906
def result_with_hash(hash)
  b = new_toplevel(hash.keys)
  hash.each_pair do |key, value|
    b.local_variable_set(key, value)
  end
  result(b)
end
            

Generate results and print them. (see #result)

 
               # File erb.rb, line 878
def run(b=new_toplevel)
  print self.result(b)
end
            

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 870
def set_eoutvar(compiler, eoutvar = '_erbout')
  compiler.put_cmd = "#{eoutvar}.<<"
  compiler.insert_cmd = "#{eoutvar}.<<"
  compiler.pre_cmd = ["#{eoutvar} = +''"]
  compiler.post_cmd = [eoutvar]
end