| Class | ERB |
| In: |
lib/erb.rb
|
| Parent: | Object |
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 %> % 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.
There are several settings you can change when you use ERB:
See the ERB.new and ERB#result methods for more detail.
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"
# Create template.
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, 0, "%<>")
# Set up template data.
to = "Community Spokesman <spokesman@ruby_community.org>"
priorities = [ "Run Ruby Quiz",
"Document Modules",
"Answer Questions on Ruby Talk" ]
# Produce result.
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
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"
# Build template data class.
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
# Create 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>
}.gsub(/^ /, '')
rhtml = ERB.new(template)
# Set up template data.
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!")
# Produce result.
rhtml.run(toy.get_binding)
Generates (some blank lines removed):
<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>
There are a variety of templating solutions available in various Ruby projects:
Rails, the web application framework, uses ERB to create views.
| Revision | = | '$Date: 2009-02-24 02:44:50 +0900 (Tue, 24 Feb 2009) $' |
| filename | [RW] | The optional filename argument passed to Kernel#eval when the ERB code is run |
| src | [R] | The Ruby code generated by 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 %>
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
end
def build
b = binding
# create and run templates, filling member data variables
ERB.new(<<-'END_PRODUCT'.gsub(/^\s+/, ""), 0, "", "@product").result b
<%= PRODUCT[:name] %>
<%= PRODUCT[:desc] %>
END_PRODUCT
ERB.new(<<-'END_PRICE'.gsub(/^\s+/, ""), 0, "", "@price").result b
<%= PRODUCT[:name] %> -- <%= PRODUCT[:cost] %>
<%= PRODUCT[:desc] %>
END_PRICE
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 lib/erb.rb, line 664
664: def initialize(str, safe_level=nil, trim_mode=nil, eoutvar='_erbout')
665: @safe_level = safe_level
666: compiler = ERB::Compiler.new(trim_mode)
667: set_eoutvar(compiler, eoutvar)
668: @src = compiler.compile(str)
669: @filename = nil
670: end
Returns revision information for the erb.rb module.
# File lib/erb.rb, line 242
242: def self.version
243: "erb.rb [2.1.0 #{ERB::Revision.split[1]}]"
244: 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 lib/erb.rb, line 763
763: def def_class(superklass=Object, methodname='result')
764: cls = Class.new(superklass)
765: def_method(cls, methodname, @filename || '(ERB)')
766: cls
767: 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 lib/erb.rb, line 730
730: def def_method(mod, methodname, fname='(ERB)')
731: mod.module_eval("def #{methodname}\n" + self.src + "\nend\n", fname, 0)
732: 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 lib/erb.rb, line 744
744: def def_module(methodname='erb')
745: mod = Module.new
746: def_method(mod, methodname, @filename || '(ERB)')
747: mod
748: end
Executes the generated ERB code to produce a completed template, returning the results of that code. (See ERB#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 lib/erb.rb, line 712
712: def result(b=TOPLEVEL_BINDING)
713: if @safe_level
714: proc {
715: $SAFE = @safe_level
716: eval(@src, b, (@filename || '(erb)'), 1)
717: }.call
718: else
719: eval(@src, b, (@filename || '(erb)'), 1)
720: end
721: end
Generate results and print them. (see ERB#result)
# File lib/erb.rb, line 700
700: def run(b=TOPLEVEL_BINDING)
701: print self.result(b)
702: 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.
# File lib/erb.rb, line 684
684: def set_eoutvar(compiler, eoutvar = '_erbout')
685: compiler.put_cmd = "#{eoutvar}.concat"
686: compiler.insert_cmd = "#{eoutvar}.concat"
687:
688: cmd = []
689: cmd.push "#{eoutvar} = ''"
690:
691: compiler.pre_cmd = cmd
692:
693: cmd = []
694: cmd.push(eoutvar)
695:
696: compiler.post_cmd = cmd
697: end