Class: ERB

Inherits:
Object
  • Object
show all
Defined in:
lib/erb.rb,
ext/erb/escape/escape.c,
lib/erb/version.rb

Overview

:markup: markdown

Class ERB (the name stands for **Embedded Ruby**) is an easy-to-use, but also very powerful, [template processor][template processor].

## Usage

Before you can use ERB, you must first require it (examples on this page assume that this has been done):

“‘ require ’erb’ “‘

## In Brief

Here’s how ERB works:

  • You can create a template: a plain-text string that includes specially formatted tags..

  • You can create an ERB object to store the template.

  • You can call instance method ERB#result to get the result.

ERB supports tags of three kinds:

  • [Expression tags][expression tags]: each begins with ‘’<%=‘`, ends with `’%>‘`; contains a Ruby expression; in the result, the value of the expression replaces the entire tag:

        template = 'The magic word is <%= magic_word %>.'
    erb = ERB.new(template)
    magic_word = 'xyzzy'
    erb.result(binding) # => "The magic word is xyzzy."

The above call to #result passes argument `binding`,
which contains the binding of variable `magic_word` to its string value `'xyzzy'`.

The below call to #result need not pass a binding,
because its expression `Date::DAYNAMES` is globally defined.

    ERB.new('Today is <%= Date::DAYNAMES[Date.today.wday] %>.').result # => "Today is Monday."

  • [Execution tags][execution tags]: each begins with ‘’<%‘`, ends with `’%>‘`; contains Ruby code to be executed:

    template = '<% File.write("t.txt", "Some stuff.") %>'
ERB.new(template).result
File.read('t.txt') # => "Some stuff."

  • [Comment tags][comment tags]: each begins with ‘’<%#‘`, ends with `’%>‘`; contains comment text; in the result, the entire tag is omitted.

    template = 'Some stuff;<%# Note to self: figure out what the stuff is. %> more stuff.'
ERB.new(template).result # => "Some stuff; more stuff."

## Some Simple Examples

Here’s a simple example of ERB in action:

“‘ template = ’The time is <%= Time.now %>.‘ erb = ERB.new(template) erb.result # => “The time is 2025-09-09 10:49:26 -0500.” “`

Details:

  1. A plain-text string is assigned to variable template. Its embedded [expression tag][expression tags] ‘’<%= Time.now %>‘` includes a Ruby expression, Time.now.

  2. The string is put into a new ERB object, and stored in variable erb.

  3. Method call erb.result generates a string that contains the run-time value of Time.now, as computed at the time of the call.

The ERB object may be re-used:

“‘ erb.result # => “The time is 2025-09-09 10:49:33 -0500.” “`

Another example:

“‘ template = ’The magic word is <%= magic_word %>.‘ erb = ERB.new(template) magic_word = ’abracadabra’ erb.result(binding) # => “The magic word is abracadabra.” “‘

Details:

  1. As before, a plain-text string is assigned to variable template. Its embedded [expression tag][expression tags] ‘’<%= magic_word %>‘` has a variable name, magic_word.

  2. The string is put into a new ERB object, and stored in variable erb; note that magic_word need not be defined before the ERB object is created.

  3. ‘magic_word = ’abracadabra’‘ assigns a value to variable magic_word.

  4. Method call ‘erb.result(binding)` generates a string that contains the value of magic_word.

As before, the ERB object may be re-used:

“‘ magic_word = ’xyzzy’ erb.result(binding) # => “The magic word is xyzzy.” “‘

## Bindings

A call to method #result, which produces the formatted result string, requires a [Binding object][binding object] as its argument.

The binding object provides the bindings for expressions in [expression tags][expression tags].

There are three ways to provide the required binding:

  • [Default binding][default binding].

  • [Local binding][local binding].

  • Augmented binding][augmented binding

### Default Binding

When you pass no binding argument to method #result, the method uses its default binding: the one returned by method #new_toplevel. This binding has the bindings defined by Ruby itself, which are those for Ruby’s constants and variables.

That binding is sufficient for an expression tag that refers only to Ruby’s constants and variables; these expression tags refer only to Ruby’s global constant RUBY_COPYRIGHT and global variable ‘$0`:

“‘ template = <<TEMPLATE The Ruby copyright is <%= RUBY_COPYRIGHT.inspect %>. The current process is <%= $0 %>. TEMPLATE puts ERB.new(template).result The Ruby copyright is “ruby - Copyright © 1993-2025 Yukihiro Matsumoto”. The current process is irb. “`

(The current process is irb because that’s where we’re doing these examples!)

### Local Binding

The default binding is not sufficient for an expression that refers to a a constant or variable that is not defined there:

“‘ Foo = 1 # Defines local constant Foo. foo = 2 # Defines local variable foo. template = <<TEMPLATE The current value of constant Foo is <%= Foo %>. The current value of variable foo is <%= foo %>. The Ruby copyright is <%= RUBY_COPYRIGHT.inspect %>. The current process is <%= $0 %>. TEMPLATE erb = ERB.new(template) “`

This call below raises NameError because although Foo and foo are defined locally, they are not defined in the default binding:

“‘ erb.result # Raises NameError. “`

To make the locally-defined constants and variables available, you can call #result with the local binding:

“‘ puts erb.result(binding) The current value of constant Foo is 1. The current value of variable foo is 2. The Ruby copyright is “ruby - Copyright © 1993-2025 Yukihiro Matsumoto”. The current process is irb. “`

### Augmented Binding

Another way to make variable bindings (but not constant bindings) available is to use method #result_with_hash(hash); the passed hash has name/value pairs that are to be used to define and assign variables in a copy of the default binding:

“‘ template = <<TEMPLATE The current value of variable bar is <%= bar %>. The current value of variable baz is <%= baz %>. The Ruby copyright is <%= RUBY_COPYRIGHT.inspect %>. The current process is <%= $0 %>. TEMPLATE erb = ERB.new(template) “`

Both of these calls raise NameError, because bar and baz are not defined in either the default binding or the local binding.

“‘ puts erb.result # Raises NameError. puts erb.result(binding) # Raises NameError. “`

This call passes a hash that causes bar and baz to be defined in a new binding (derived from #new_toplevel):

“‘ hash = 3, baz: 4 puts erb.result_with_hash(hash) The current value of variable bar is 3. The current value of variable baz is 4. The Ruby copyright is “ruby - Copyright © 1993-2025 Yukihiro Matsumoto”. The current process is irb. “`

## Tags

The examples above use expression tags. These are the tags available in ERB:

  • [Expression tag][expression tags]: the tag contains a Ruby expression; in the result, the entire tag is to be replaced with the run-time value of the expression.

  • [Execution tag][execution tags]: the tag contains Ruby code; in the result, the entire tag is to be replaced with the run-time value of the code.

  • [Comment tag][comment tags]: the tag contains comment code; in the result, the entire tag is to be omitted.

### Expression Tags

You can embed a Ruby expression in a template using an *expression tag*.

Its syntax is ‘<%= expression %>`, where expression is any valid Ruby expression.

When you call method #result, the method evaluates the expression and replaces the entire expression tag with the expression’s value:

“‘ ERB.new(’Today is <%= Date::DAYNAMES %>.‘).result # => “Today is Monday.” ERB.new(’Tomorrow will be <%= Date::DAYNAMES[Date.today.wday + 1] %>.‘).result # => “Tomorrow will be Tuesday.” ERB.new(’Yesterday was <%= Date::DAYNAMES[Date.today.wday - 1] %>.‘).result # => “Yesterday was Sunday.” “`

Note that whitespace before and after the expression is allowed but not required, and that such whitespace is stripped from the result.

“‘ ERB.new(’My appointment is on <%=Date::DAYNAMES[Date.today.wday + 2]%>.‘).result # => “My appointment is on Wednesday.” ERB.new(’My appointment is on <%= Date::DAYNAMES[Date.today.wday + 2] %>.‘).result # => “My appointment is on Wednesday.” “`

### Execution Tags

You can embed Ruby executable code in template using an *execution tag*.

Its syntax is ‘<% code %>`, where code is any valid Ruby code.

When you call method #result, the method executes the code and removes the entire execution tag (generating no text in the result):

“‘ ERB.new(’foo <% Dir.chdir(“C:/”) %> bar’).result # => “foo bar” “‘

Whitespace before and after the embedded code is optional:

“‘ ERB.new(’foo <%Dir.chdir(“C:/”)%> bar’).result # => “foo bar” “‘

You can interleave text with execution tags to form a control structure such as a conditional, a loop, or a case statements.

Conditional:

“‘ template = <<TEMPLATE <% if verbosity %> An error has occurred. <% else %> Oops! <% end %> TEMPLATE erb = ERB.new(template) verbosity = true erb.result(binding) # => “nAn error has occurred.nn” verbosity = false erb.result(binding) # => “nOops!nn” “`

Note that the interleaved text may itself contain expression tags:

Loop:

“‘ template = <<TEMPLATE <% Date::ABBR_DAYNAMES.each do |dayname| %> <%= dayname %> <% end %> TEMPLATE ERB.new(template).result # => “nSunnnMonnnTuennWednnThunnFrinnSatnn” “`

Other, non-control, lines of Ruby code may be interleaved with the text, and the Ruby code may itself contain regular Ruby comments:

“‘ template = <<TEMPLATE <% 3.times do %> <%= Time.now %> <% sleep(1) # Let’s make the times different. %> <% end %> TEMPLATE ERB.new(template).result # => “n2025-09-09 11:36:02 -0500nnn2025-09-09 11:36:03 -0500nnn2025-09-09 11:36:04 -0500nnn” “‘

The execution tag may also contain multiple lines of code:

“‘ template = <<TEMPLATE <%

(0..2).each do |i|
  (0..2).each do |j|

%>

  • <%=i%>,<%=j%>

<%

  end
end

%> TEMPLATE ERB.new(template).result # => “n* 0,0nn* 0,1nn* 0,2nn* 1,0nn* 1,1nn* 1,2nn* 2,0nn* 2,1nn* 2,2nn” “‘

#### Shorthand Format for Execution Tags

You can use keyword argument ‘trim_mode: ’%‘` to enable a shorthand format for execution tags; this example uses the shorthand format `% code` instead of `<% code %>`:

“‘ template = <<TEMPLATE % priorities.each do |priority|

* <%= priority %>

% end TEMPLATE erb = ERB.new(template, trim_mode: ‘%’) priorities = [ ‘Run Ruby Quiz’,

'Document Modules',
'Answer Questions on Ruby Talk' ]

puts erb.result(binding)

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

“‘

Note that in the shorthand format, the character ‘’%‘` must be the first character in the code line (no leading whitespace).

#### Suppressing Unwanted Blank Lines

With keyword argument trim_mode not given, all blank lines go into the result:

“‘ template = <<TEMPLATE <% if true %> <%= RUBY_VERSION %> <% end %> TEMPLATE ERB.new(template).result.lines.each {|line| puts line.inspect } “n” “3.4.5n” “n” “`

You can give ‘trim_mode: ’-‘`, you can suppress each blank line whose source line ends with `-%>` (instead of `%>`):

“‘ template = <<TEMPLATE <% if true -%> <%= RUBY_VERSION %> <% end -%> TEMPLATE ERB.new(template, trim_mode: ’-‘).result.lines.each {|line| puts line.inspect } “3.4.5n” “`

It is an error to use the trailing ‘’-%>‘` notation without `trim_mode: ’-‘`:

“‘ ERB.new(template).result.lines.each {|line| puts line.inspect } # Raises SyntaxError. “`

#### Suppressing Unwanted Newlines

Consider this template:

“‘ template = <<TEMPLATE <% RUBY_VERSION %> <%= RUBY_VERSION %> foo <% RUBY_VERSION %> foo <%= RUBY_VERSION %> TEMPLATE “`

With keyword argument trim_mode not given, all newlines go into the result:

“‘ ERB.new(template).result.lines.each {|line| puts line.inspect } “n” “3.4.5n” “foo n” “foo 3.4.5n” “`

You can give ‘trim_mode: ’>‘` to suppress the trailing newline for each line that ends with `’%>‘` (regardless of its beginning):

“‘ ERB.new(template, trim_mode: ’>‘).result.lines.each {|line| puts line.inspect } “3.4.5foo foo 3.4.5” “`

You can give ‘trim_mode: ’<>‘` to suppress the trailing newline for each line that both begins with `’<%‘` and ends with `’%>‘`:

“‘ ERB.new(template, trim_mode: ’<>‘).result.lines.each {|line| puts line.inspect } “3.4.5foo n” “foo 3.4.5n” “`

#### Combining Trim Modes

You can combine certain trim modes:

  • ‘’%-‘`: Enable shorthand and omit each blank line ending with `’-%>‘`.

  • ‘’%>‘`: Enable shorthand and omit newline for each line ending with `’%>‘`.

  • ‘’%<>‘`: Enable shorthand and omit newline for each line starting with `’<%‘` and ending with `’%>‘`.

### Comment Tags

You can embed a comment in a template using a *comment tag*; its syntax is ‘<%# text %>`, where text is the text of the comment.

When you call method #result, it removes the entire comment tag (generating no text in the result).

Example:

“‘ template = ’Some stuff;<%# Note to self: figure out what the stuff is. %> more stuff.‘ ERB.new(template).result # => “Some stuff; more stuff.” “`

A comment tag may appear anywhere in the template.

Note that the beginning of the tag must be ‘’<%#‘`, not `’<% #‘`.

In this example, the tag begins with ‘’<% #‘`, and so is an execution tag, not a comment tag; the cited code consists entirely of a Ruby-style comment (which is of course ignored):

“‘ ERB.new(’Some stuff;<% # Note to self: figure out what the stuff is. %> more stuff.‘).result # => “Some stuff;” “`

## Encodings

An ERB object has an [encoding], which is by default the encoding of the template string; the result string will also have that encoding.

“‘ template = <<TEMPLATE <%# Comment. %> TEMPLATE erb = ERB.new(template) template.encoding # => #<Encoding:UTF-8> erb.encoding # => #<Encoding:UTF-8> erb.result.encoding # => #<Encoding:UTF-8> “`

You can specify a different encoding by adding a [magic comment][magic comments] at the top of the given template:

“‘ template = <<TEMPLATE <%#-*- coding: Big5 -*-%> <%# Comment. %> TEMPLATE erb = ERB.new(template) template.encoding # => #<Encoding:UTF-8> erb.encoding # => #<Encoding:Big5> erb.result.encoding # => #<Encoding:Big5> “`

## Error Reporting

Consider this template (containing an error):

“‘ template = ’<%= nosuch %>‘ erb = ERB.new(template) “`

When ERB reports an error, it includes a file name (if available) and a line number; the file name comes from method #filename, the line number from method #lineno.

Initially, those values are nil and 0, respectively; these initial values are reported as ‘’(erb)‘` and 1, respectively:

“‘ erb.filename # => nil erb.lineno # => 0 erb.result (erb):1:in ’<main>‘: undefined local variable or method ’nosuch’ for main (NameError) “‘

You can use methods #filename= and #lineno= to assign values that are more meaningful in your context:

“‘ erb.filename = ’t.txt’ erb.lineno = 555 erb.result t.txt:556:in ‘<main>’: undefined local variable or method ‘nosuch’ for main (NameError) “‘

You can use method #location= to set both values:

“‘ erb.location = [’u.txt’, 999] erb.result u.txt:1000:in ‘<main>’: undefined local variable or method ‘nosuch’ for main (NameError) “‘

## Plain Text with Embedded Ruby

Here’s a plain-text template; it uses the literal notation ‘’%q{ … }‘` to define the template (see [%q literals][%q literals]); this avoids problems with backslashes.

“‘ template = %q{ From: James Edward Gray II <[email protected]> To: <%= to %> Subject: Addressing Needs

<%= to %>:

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 } “‘

The template will need these:

“‘ to = ’Community Spokesman <spokesman@ruby_community.org>‘ priorities = [ ’Run Ruby Quiz’,

'Document Modules',
'Answer Questions on Ruby Talk' ]

“‘

Finally, create the ERB object and get the result

“‘ erb = ERB.new(template, trim_mode: ’%<>‘) puts erb.result(binding)

From: James Edward Gray II <[email protected]> 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 “‘

## HTML with Embedded Ruby

This example shows an HTML template.

First, here’s a custom class, Product:

“‘ 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

# Support templating of member data.
def get_binding
  binding
end

end “‘

The template below will need these values:

“‘ 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!’) “‘

Here’s the HTML:

“‘ template = <<TEMPLATE <html>

<head><title>Ruby Toys -- <%= @name %></title></head>
<body>
  <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>

</html> TEMPLATE “‘

Finally, create the ERB object and get the result (omitting some blank lines):

“‘ erb = ERB.new(template) puts erb.result(toy.get_binding) <html>

<head><title>Ruby Toys -- Rubysapien</title></head>
<body>
  <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>
</body>

</html> “‘

## Other Template Processors

Various Ruby projects have their own template processors. The Ruby Processing System [RDoc], for example, has one that can be used elsewhere.

Other popular template processors may found in the [Template Engines][template engines] page of the Ruby Toolbox.

[%q literals]: docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-25q-3A+Non-Interpolable+String+Literals [augmented binding]: ERB@Augmented+Binding [binding object]: docs.ruby-lang.org/en/master/Binding.html [comment tags]: ERB@Comment+Tags [default binding]: ERB@Default+Binding [encoding]: docs.ruby-lang.org/en/master/Encoding.html [execution tags]: ERB@Execution+Tags [expression tags]: ERB@Expression+Tags [kernel#binding]: docs.ruby-lang.org/en/master/Kernel.html#method-i-binding [local binding]: ERB@Local+Binding [magic comments]: docs.ruby-lang.org/en/master/syntax/comments_rdoc.html#label-Magic+Comments [rdoc]: ruby.github.io/rdoc [sprintf]: docs.ruby-lang.org/en/master/Kernel.html#method-i-sprintf [template engines]: www.ruby-toolbox.com/categories/template_engines [template processor]: en.wikipedia.org/wiki/Template_processor

Defined Under Namespace

Modules: DefMethod, Escape, Util Classes: Compiler

Constant Summary collapse

VERSION =

The string ERB version.

'6.0.1'

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(str, trim_mode: nil, eoutvar: '_erbout') ⇒ ERB

:markup: markdown

:call-seq:

ERB.new(template, trim_mode: nil, eoutvar: '_erbout')

Returns a new ERB object containing the given string template.

For details about template, its embedded tags, and generated results, see ERB.

**Keyword Argument trim_mode**

You can use keyword argument ‘trim_mode: ’%‘` to enable the [shorthand format][shorthand format] for execution tags.

This value allows [blank line control][blank line control]:

  • ‘’-‘`: Omit each blank line ending with `’%>‘`.

Other values allow [newline control][newline control]:

  • ‘’>‘`: Omit newline for each line ending with `’%>‘`.

  • ‘’<>‘`: Omit newline for each line starting with `’<%‘` and ending with `’%>‘`.

You can also [combine trim modes][combine trim modes].

**Keyword Argument eoutvar**

The string value of keyword argument eoutvar specifies the name of the variable that method #result uses to construct its result string; see #src.

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.

It’s good practice to choose a variable name that begins with an underscore: ‘’_’‘.

[blank line control]: ERB@Suppressing+Unwanted+Blank+Lines [combine trim modes]: ERB@Combining+Trim+Modes [newline control]: ERB@Suppressing+Unwanted+Newlines [shorthand format]: ERB@Shorthand+Format+for+Execution+Tags



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# File 'lib/erb.rb', line 832

def initialize(str, trim_mode: nil, eoutvar: '_erbout')
  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

Instance Attribute Details

#encoding ⇒ Object (readonly)

:markup: markdown

Returns the encoding of self; see [Encodings]:

[encodings]: ERB@Encodings



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# File 'lib/erb.rb', line 909

def encoding
  @encoding
end

#filename ⇒ Object

:markup: markdown

Sets or returns the file name to be used in reporting errors; see [Error Reporting][error reporting].

[error reporting]: ERB@Error+Reporting



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# File 'lib/erb.rb', line 917

def filename
  @filename
end

#lineno ⇒ Object

:markup: markdown

Sets or returns the line number to be used in reporting errors; see [Error Reporting][error reporting].

[error reporting]: ERB@Error+Reporting



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# File 'lib/erb.rb', line 925

def lineno
  @lineno
end

#src ⇒ Object (readonly)

:markup: markdown

Returns the Ruby code that, when executed, generates the result; the code is executed by method #result, and by its wrapper methods #result_with_hash and #run:

“‘ template = ’The time is <%= Time.now %>.‘ erb = ERB.new(template) erb.src # => “#coding:UTF-8n_erbout = +”; _erbout.<< "The time is ".freeze; _erbout.<<(( Time.now ).to_s); _erbout.<< ".".freeze; _erbout” erb.result # => “The time is 2025-09-18 15:58:08 -0500.” “`

In a more readable format:

“‘

# puts erb.src.split('; ')
# #coding:UTF-8
# _erbout = +''
# _erbout.<< "The time is ".freeze
# _erbout.<<(( Time.now ).to_s)
# _erbout.<< ".".freeze
# _erbout

“‘

Variable _erbout is used to store the intermediate results in the code; the name _erbout is the default in ERB.new, and can be changed via keyword argument eoutvar:

“‘ erb = ERB.new(template, eoutvar: ’_foo’) puts template.src.split(‘; ’) #coding:UTF-8 _foo = +” _foo.<< “The time is ”.freeze _foo.<<(( Time.now ).to_s) _foo.<< “.”.freeze _foo “‘



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# File 'lib/erb.rb', line 900

def src
  @src
end

Class Method Details

.version ⇒ Object

:markup: markdown

:call-seq:

self.version -> string

Returns the string ERB version.



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# File 'lib/erb.rb', line 787

def self.version
  VERSION
end

Instance Method Details

#def_class(superklass = Object, methodname = 'result') ⇒ Object

:markup: markdown

:call-seq:

def_class(super_class = Object, method_name = 'result') -> new_class

Returns a new nameless class whose superclass is super_class, and which has instance method method_name.

Create a template from HTML that has embedded expression tags that use ‘@arg1` and `@arg2`:

“‘ html = <<TEMPLATE <html> <body>

<p><%= @arg1 %></p>
<p><%= @arg2 %></p>

</body> </html> TEMPLATE template = ERB.new(html) “‘

Create a base class that has ‘@arg1` and `@arg2`:

“‘ class MyBaseClass

def initialize(arg1, arg2)
  @arg1 = arg1
  @arg2 = arg2
end

end “‘

Use method #def_class to create a subclass that has method :render:

“‘ MySubClass = template.def_class(MyBaseClass, :render) “`

Generate the result:

“‘ puts MySubClass.new(’foo’, 123).render <html> <body>

<p>foo</p>
<p>123</p>

</body> </html> “‘



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# File 'lib/erb.rb', line 1170

def def_class(superklass=Object, methodname='result')
  cls = Class.new(superklass)
  def_method(cls, methodname, @filename || '(ERB)')
  cls
end

#def_method(mod, methodname, fname = '(ERB)') ⇒ Object

:markup: markdown

:call-seq:

def_method(module, method_signature, filename = '(ERB)') -> method_name

Creates and returns a new instance method in the given module module; returns the method name as a symbol.

The method is created from the given method_signature, which consists of the method name and its argument names (if any).

The filename sets the value of #filename; see [Error Reporting][error reporting].

[error reporting]: ERB@Error+Reporting

“‘ template = ’<%= arg1 %> <%= arg2 %>‘ erb = ERB.new(template) MyModule = Module.new erb.def_method(MyModule, ’render(arg1, arg2)‘) # => :render class MyClass; include MyModule; end MyClass.new.render(’foo’, 123) # => “foo 123” “‘



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# File 'lib/erb.rb', line 1088

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

#def_module(methodname = 'erb') ⇒ Object

:markup: markdown

:call-seq:

def_module(method_name = 'erb') -> new_module

Returns a new nameless module that has instance method method_name.

“‘ template = ’<%= arg1 %> <%= arg2 %>‘ erb = ERB.new(template) MyModule = template.def_module(’render(arg1, arg2)‘) class MyClass

include MyModule

end MyClass.new.render(‘foo’, 123) # => “foo 123” “‘



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# File 'lib/erb.rb', line 1113

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

#location=(filename, lineno) ⇒ Object

:markup: markdown

:call-seq:

location = [filename, lineno] => [filename, lineno]
location = filename -> filename

Sets the values of #filename and, if given, #lineno; see [Error Reporting][error reporting].

[error reporting]: ERB@Error+Reporting



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# File 'lib/erb.rb', line 937

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

#make_compiler(trim_mode) ⇒ Object

:markup: markdown

:call-seq:

make_compiler -> erb_compiler

Returns a new ERB::Compiler with the given trim_mode; for trim_mode values, see ERB.new:

“‘ ERB.new(”).make_compiler(nil) # => #<ERB::Compiler:0x000001cff9467678 @insert_cmd=“print”, @percent=false, @post_cmd=[], @pre_cmd=[], @put_cmd=“print”, @trim_mode=nil> “`



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# File 'lib/erb.rb', line 854

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

#result(b = new_toplevel) ⇒ Object

:markup: markdown

:call-seq:

result(binding = new_toplevel) -> new_string

Returns the string result formed by processing ERB tags found in the stored template in self.

With no argument given, uses the default binding; see [Default Binding][default binding].

With argument binding given, uses the local binding; see [Local Binding][local binding].

See also #result_with_hash.

[default binding]: ERB@Default+Binding [local binding]: ERB@Local+Binding



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# File 'lib/erb.rb', line 1008

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

#result_with_hash(hash) ⇒ Object

:markup: markdown

:call-seq:

result_with_hash(hash) -> new_string

Returns the string result formed by processing ERB tags found in the stored string in self; see [Augmented Binding][augmented binding].

See also #result.

[augmented binding]: ERB@Augmented+Binding



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# File 'lib/erb.rb', line 1027

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

#run(b = new_toplevel) ⇒ Object

:markup: markdown

:call-seq:

run(binding = new_toplevel) -> nil

Like #result, but prints the result string (instead of returning it); returns nil.



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# File 'lib/erb.rb', line 986

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

#set_eoutvar(compiler, eoutvar = '_erbout') ⇒ Object

:markup: markdown

:call-seq:

set_eoutvar(compiler, eoutvar = '_erbout') -> [eoutvar]

Sets the eoutvar value in the ERB::Compiler object compiler; returns a 1-element array containing the value of eoutvar:

“‘ template = ERB.new(”) compiler = template.make_compiler(nil) pp compiler #<ERB::Compiler:0x000001cff8a9aa00

@insert_cmd="print",
@percent=false,
@post_cmd=[],
@pre_cmd=[],
@put_cmd="print",
@trim_mode=nil>

template.set_eoutvar(compiler, ‘_foo’) # => [“_foo”] pp compiler #<ERB::Compiler:0x000001cff8a9aa00

@insert_cmd="_foo.<<",
@percent=false,
@post_cmd=["_foo"],
@pre_cmd=["_foo = +''"],
@put_cmd="_foo.<<",
@trim_mode=nil>

“‘



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# File 'lib/erb.rb', line 972

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