class ERB

ERB – Ruby 模板 ↑

简介 ↑

ERB 为 Ruby 提供了一个易于使用但功能强大的模板系统。 使用 ERB，可以将实际的 Ruby 代码添加到任何纯文本文档中，以生成文档信息详细信息和/或流程控制。

一个非常简单的例子是这样

require 'erb'

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

输出: x 的值是: 42

下面给出了更复杂的例子。

识别的标签 ↑

ERB 识别提供的模板中的某些标签，并根据以下规则转换它们

<% 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

所有其他文本都通过 ERB 过滤，保持不变。

选项 ↑

使用 ERB 时，可以更改几个设置

有关更多详细信息，请参阅 ERB.new 和 ERB#result 方法。

字符编码 ↑

ERB（或由 ERB 生成的 Ruby 代码）返回与输入字符串具有相同字符编码的字符串。 但是，当输入字符串具有魔术注释时，它将返回使用魔术注释指定的编码的字符串。

# -*- coding: utf-8 -*-
require 'erb'

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

输出: _ENCODING_ 是 Big5。

示例 ↑

纯文本 ↑

ERB 适用于任何通用模板的情况。 请注意，在此示例中，我们使用了方便的“行首 %”标记，并且我们使用 %q{...} 字面量引用模板，以避免反斜杠的麻烦。

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, trim_mode: "%<>")

# 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

生成

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

HTML 中的 Ruby ↑

ERB 通常用于 .rhtml 文件（嵌入 Ruby 的 HTML）。 请注意，在此示例中，当运行模板时需要提供特殊的绑定，以便可以解析 Product 对象中的实例变量。

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)

生成（删除了一些空白行）

<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>

注意 ↑

在各种 Ruby 项目中提供了多种模板解决方案。 例如，与 Ruby 一起分发的 RDoc 使用它自己的模板引擎，该引擎可以在其他地方重用。

其他流行的引擎可以在 Ruby 工具箱的相应 类别中找到。