class ERB - Documentation for Ruby 3.5 (original) (raw)

ERB – Ruby Templating¶ ↑

Introduction¶ ↑

ERB provides an easy to use but powerful templating system for Ruby. Using ERB, actual Ruby code can be added to any plain text document for the purposes of generating document information details and/or flow control.

A very simple example is this:

require 'erb'

x = 42 template = ERB.new <<-EOF The value of x is: <%= x %> EOF puts template.result(binding)

Prints: The value of x is: 42

More complex examples are given below.

ERB recognizes certain tags in the provided template and converts them based on the rules below:

<% Ruby code -- inline with output %> <%= Ruby expression -- replace with result %> <%# comment -- ignored -- useful in testing %> (<% # doesn't work. Don't use Ruby comments.) % a line of Ruby code -- treated as <% line %> (optional -- see ERB.new) %% replaced with % if first thing on a line and % processing is used <%% or %%> -- replace with <% or %> respectively

All other text is passed through ERB filtering unchanged.

Options¶ ↑

There are several settings you can change when you use ERB:

the nature of the tags that are recognized;
the binding used to resolve local variables in the template.

See the ERB.new and ERB#result methods for more detail.

Character encodings¶ ↑

ERB (or Ruby code generated by ERB) returns a string in the same character encoding as the input string. When the input string has a magic comment, however, it returns a string in the encoding specified by the magic comment.

require 'erb'

template = ERB.new <<EOF <%#-*- coding: Big5 -*-%> __ENCODING__ is <%= __ENCODING__ %>. EOF puts template.result

Prints: _ ENCODING_ is Big5.

Examples¶ ↑

Plain Text¶ ↑

ERB is useful for any generic templating situation. Note that in this example, we use the convenient “% at start of line” tag, and we quote the template literally with %q{...} to avoid trouble with the backslash.

require "erb"

template = %q{ From: James Edward Gray II james@grayproductions.net To: <%= to %> Subject: Addressing Needs

<%= to[/\w+/] %>:

Just wanted to send a quick note assuring that your needs are being addressed.

I want you to know that my team will keep working on the issues, especially:

<%# ignore numerous minor requests -- focus on priorities %> % priorities.each do |priority| * <%= priority %> % end

Thanks for your patience.

James Edward Gray II }.gsub(/^ /, '')

message = ERB.new(template, trim_mode: "%<>")

to = "Community Spokesman <spokesman@ruby_community.org>" priorities = [ "Run Ruby Quiz", "Document Modules", "Answer Questions on Ruby Talk" ]

email = message.result puts email

Generates:

From: James Edward Gray II james@grayproductions.net To: Community Spokesman <spokesman@ruby_community.org> Subject: Addressing Needs

Community:

Just wanted to send a quick note assuring that your needs are being addressed.

I want you to know that my team will keep working on the issues, especially:

* Run Ruby Quiz
* Document Modules
* Answer Questions on Ruby Talk

Thanks for your patience.

James Edward Gray II

Ruby in HTML¶ ↑

ERB is often used in .rhtml files (HTML with embedded Ruby). Notice the need in this example to provide a special binding when the template is run, so that the instance variables in the Product object can be resolved.

require "erb"

class Product def initialize( code, name, desc, cost ) @code = code @name = name @desc = desc @cost = cost

@features = [ ]

end

def add_feature( feature ) @features << feature end

def get_binding binding end

end

template = %{ Ruby Toys -- <%= @name %>

  <h1><%= @name %> (<%= @code %>)</h1>
  <p><%= @desc %></p>

  <ul>
    <% @features.each do |f| %>
      <li><b><%= f %></b></li>
    <% end %>
  </ul>

  <p>
    <% if @cost < 10 %>
      <b>Only <%= @cost %>!!!</b>
    <% else %>
       Call for a price, today!
    <% end %>
  </p>

</body>

}.gsub(/^ /, '')

rhtml = ERB.new(template)

toy = Product.new( "TZ-1002", "Rubysapien", "Geek's Best Friend! Responds to Ruby commands...", 999.95 ) toy.add_feature("Listens for verbal commands in the Ruby language!") toy.add_feature("Ignores Perl, Java, and all C variants.") toy.add_feature("Karate-Chop Action!!!") toy.add_feature("Matz signature on left leg.") toy.add_feature("Gem studded eyes... Rubies, of course!")

rhtml.run(toy.get_binding)

Generates (some blank lines removed):

Ruby Toys -- Rubysapien

<h1>Rubysapien (TZ-1002)</h1>
<p>Geek's Best Friend!  Responds to Ruby commands...</p>

<ul>
    <li><b>Listens for verbal commands in the Ruby language!</b></li>
    <li><b>Ignores Perl, Java, and all C variants.</b></li>
    <li><b>Karate-Chop Action!!!</b></li>
    <li><b>Matz signature on left leg.</b></li>
    <li><b>Gem studded eyes... Rubies, of course!</b></li>
</ul>

<p>
     Call for a price, today!
</p>

Notes¶ ↑

There are a variety of templating solutions available in various Ruby projects. For example, RDoc, distributed with Ruby, uses its own template engine, which can be reused elsewhere.

Other popular engines could be found in the corresponding Category of The Ruby Toolbox.

Constants

NOT_GIVEN

VERSION

Attributes

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

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

The Ruby code generated by ERB

Public Class Methods

Source

def initialize(str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eoutvar=NOT_GIVEN, trim_mode: nil, eoutvar: '_erbout')

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 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 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 eoutvar = legacy_eoutvar end

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

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 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"

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

attr_reader :product, :price

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

def build b = binding

ERB.new(<<~'END_PRODUCT', trim_mode: "", eoutvar: "@product").result b
  <%= PRODUCT[:name] %>
  <%= PRODUCT[:desc] %>
END_PRODUCT
ERB.new(<<~'END_PRICE', trim_mode: "", eoutvar: "@price").result b
  <%= PRODUCT[:name] %> -- <%= PRODUCT[:cost] %>
  <%= PRODUCT[:desc] %>
END_PRICE

end end

listings = Listings.new listings.build

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

Generates

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

Chicken Fried Steak -- 9.95 A well massaged pattie, breaded and fried.

Source

def self.version VERSION end

Returns revision information for the erb.rb module.

Public Instance Methods

Source

def def_class(superklass=Object, methodname='result') cls = Class.new(superklass) def_method(cls, methodname, @filename || '(ERB)') cls 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'
erb = ERB.new(File.read(filename)) erb.filename = filename MyClass = erb.def_class(MyClass_, 'render()') print MyClass.new('foo', 123).render()

Source

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

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

example:

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

Source

def def_module(methodname='erb') mod = Module.new def_method(mod, methodname, @filename || '(ERB)') mod end

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

example:

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

Source

def location=((filename, lineno)) @filename = filename @lineno = lineno if lineno end

Sets optional filename and line number that will be used in ERB code evaluation and error reporting. See also filename= and lineno=

erb = ERB.new('<%= some_x %>') erb.render

erb.location = ['file.erb', 3]

erb.render

Source

def make_compiler(trim_mode) ERB::Compiler.new(trim_mode) end

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

Source

def result(b=new_toplevel) unless @_init.equal?(self.class.singleton_class) raise ArgumentError, "not initialized" end eval(@src, b, (@filename || '(erb)'), @lineno) end

Executes the generated ERB code to produce a completed template, returning the results of that code.

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

Source

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

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

Source

def run(b=new_toplevel) print self.result(b) end

Generate results and print them. (see ERB#result)

Source

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

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

Private Instance Methods

Source

def new_toplevel(vars = nil) b = TOPLEVEL_BINDING if vars vars = vars.select {|v| b.local_variable_defined?(v)} unless vars.empty? return b.eval("tap {|;#{vars.join(',')}| break binding}") end end b.dup end

Returns a new binding each time near TOPLEVEL_BINDING for runs that do not specify a binding.