# 30 lines implementation of eRuby

**URL:** <https://www.ruby-forum.com/t/30-lines-implementation-of-eruby/119219>\
**Category:** Ruby\
**Created:** [November 5, 2007, 3:17am UTC](https://www.ruby-forum.com/t/30-lines-implementation-of-eruby/119219 "2007-11-05T03:17:49Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![makoto\_kuwata](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a4c791/32.png) [@makoto\_kuwata](https://www.ruby-forum.com/u/makoto_kuwata)\
**Post date:** [November 5, 2007, 3:17am UTC](https://www.ruby-forum.com/t/30-lines-implementation-of-eruby/119219/1 "2007-11-05T03:17:49Z")

</div>

Hi all,

Do you like eRuby? Do you want to customize ERB?

The following is 30 lines implementation of eRuby.  
This will help you to get your own eRuby implementation.

```
class TinyEruby

  def initialize(input=nil)
    @src = convert(input) if input
  end

  attr_reader :src

  def convert(input)
    src = "_buf = '';" # preamble
    input.scan(/(.*?)<%(=)?(.*?)%>/m) do |text, ch, code|
      src << " _buf << '#{escape_text(text)}';" unless text.empty?
      src << (ch == '=' ? " _buf << (#{code}).to_s" : code) << ';'
    end
    rest = $' || input
    src << " _buf << '#{escape_text(rest)}';" unless rest.empty?
    src << "\n_buf.to_s\n" # postamble
    return src
  end

  def escape_text(text)
    return text.gsub!(/['\\]/, '\\\\\&') || text
  end

  def result(_binding=TOPLEVEL_BINDING)
    eval @src, _binding
  end

end

```

Usage of TinyEruby is the same as ERB.

The above code may be slow in some cases, because long pattern  
matching (‘(.\*?)’ and $1) in convert() is not fast.  
You can improve performance of TinyEruby to avoid long matching.

```
 ...
  def convert(input)
    src = "_buf = '';" # preamble
    pos = 0
    input.scan(/<%(=)?(.*?)%>/m) do |ch, code|
      match = Regexp.last_match
      len = match.begin(0) - pos
      text = input[pos, len]
      pos = match.end(0)
      src << " _buf << '#{escape_text(text)}';" unless text.empty?
      src << (ch == '=' ? " _buf << (#{code}).to_s" : code) << ';'
    end
    rest = $' || input
    src << " _buf << '#{escape_text(rest)}';" unless rest.empty?
    src << "\n_buf.to_s\n" # postamble
    return src
  end
  ...

```

These codes are released in public domain. You can use it freely.  
See  
[http://www.kuwata-lab.com/support/2007/10/09/30-lines-implementation-of-eruby/](http://www.kuwata-lab.com/support/2007/10/09/30-lines-implementation-of-eruby/)  
for details.