Easy Diffing in Ruby
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Diffy - Easy Diffing With Ruby

Need diffs in your ruby app? Diffy has you covered. It provides a convenient way to generate a diff from two strings or files. Instead of reimplementing the LCS diff algorithm Diffy uses battle tested Unix diff to generate diffs, and focuses on providing a convenient interface, and getting out of your way.

Supported Formats

It provides several built in format options which can be passed to Diffy::Diff#to_s.

  • :text - Plain text output
  • :color - ANSI colorized text suitable for use in a terminal
  • :html - HTML output. Since version 2.0 this format does inline highlighting of the changes between two the changes within lines.
  • :html_simple - HTML output without inline highlighting. This may be useful in situations where high performance is required or simpler output is desired.

A default format can be set like so:

Diffy::Diff.default_format = :html

Getting Started

sudo gem install diffy

Here's an example of using Diffy to diff two strings

$ irb
>> string1 = <<-TXT
>" Hello how are you
>" I'm fine
>" That's great
>" TXT
=> "Hello how are you\nI'm fine\nThat's great\n"
>> string2 = <<-TXT
>" Hello how are you?
>" I'm fine
>" That's swell
>" TXT
=> "Hello how are you?\nI'm fine\nThat's swell\n"
>> puts Diffy::Diff.new(string1, string2)
-Hello how are you
+Hello how are you?
 I'm fine
-That's great
+That's swell

HTML Output

Outputing the diff as html is easy too. Here's an example using the :html_simple formatter.

>> puts Diffy::Diff.new(string1, string2).to_s(:html_simple)
<div class="diff">
    <li class="del"><del>Hello how are you</del></li>
    <li class="ins"><ins>Hello how are you?</ins></li>
    <li class="unchanged"><span>I'm fine</span></li>
    <li class="del"><del>That's great</del></li>
    <li class="ins"><ins>That's swell</ins></li>

The :html formatter will give you inline highlighting a la github.

>> puts Diffy::Diff.new("foo\n", "Foo\n").to_s(:html)
<div class="diff">
    <li class="del"><del><strong>f</strong>oo</del></li>
    <li class="ins"><ins><strong>F</strong>oo</ins></li>

There's some pretty nice css provided in Diffy::CSS.

>> puts Diffy::CSS
.diff ul{background:#fff;overflow:auto;font-size:13px;list-style:none;margin:0;padding:0;display:table;width:100%;}
.diff del, .diff ins{display:block;text-decoration:none;}
.diff li{padding:0; display:table-row;margin: 0;height:1em;}
.diff li.ins{background:#dfd; color:#080}
.diff li.del{background:#fee; color:#b00}
.diff li:hover{background:#ffc}
/* try 'whitespace:pre;' if you don't want lines to wrap */
.diff del, .diff ins, .diff span{white-space:pre-wrap;font-family:courier;}
.diff del strong{font-weight:normal;background:#fcc;}
.diff ins strong{font-weight:normal;background:#9f9;}
.diff li.diff-comment { display: none; }
.diff li.diff-block-info { background: none repeat scroll 0 0 gray; }

Other Diff Options

Diffing files instead of strings

You can diff files instead of strings by using the :source option.

>> puts Diffy::Diff.new('/tmp/foo', '/tmp/bar', :source => 'files')

Full Diff Output

By default diffy removes the superfluous diff output. This is because its default is to show the complete diff'ed file (diff -U 10000 is the default).

Diffy does support full output, just use the :include_diff_info => true option when initializing:

>> Diffy::Diff.new("foo\nbar\n", "foo\nbar\nbaz\n", :include_diff_info => true).to_s(:text)
=>--- /Users/chaffeqa/Projects/stiwiki/tmp/diffy20111116-82153-ie27ex	2011-11-16 20:16:41.000000000 -0500
+++ /Users/chaffeqa/Projects/stiwiki/tmp/diffy20111116-82153-wzrhw5	2011-11-16 20:16:41.000000000 -0500
@@ -1,2 +1,3 @@

And even deals a bit with the formatting!

Empty Diff Behavior

By default diffy will return the full text of its first input if there are no differences with the second input. Sometimes it's useful to return the actual diff, the empty string, in this case. To enable this behavior, simply use the :allow_empty_diff => true option when initializing.

Plus and Minus symbols in HTML output

By default Diffy doesn't include the +, -, and at the beginning of line for HTML output.

You can use the :include_plus_and_minus_in_html option to include those symbols in the output.

>> puts Diffy::Diff.new(string1, string2, :include_plus_and_minus_in_html => true).to_s(:html_simple)
<div class="diff">
    <li class="del"><del><span class="symbol">-</span>Hello how are you</del></li>
    <li class="ins"><ins><span class="symbol">+</span>Hello how are you?</ins></li>
    <li class="unchanged"><span class="symbol"> </span><span>I'm fine</span></li>
    <li class="del"><del><span class="symbol">-</span>That's great</del></li>
    <li class="ins"><ins><span class="symbol">+</span>That's swell</ins></li>

Overriding the command line options passed to diff.

You can use the :diff option to override the command line options that are passed to unix diff. They default to -U 10000.

>> puts Diffy::Diff.new(" foo\nbar\n", "foo\nbar\n", :diff => "-w")

Default Diff Options

You can set the default options for new Diffy::Diffs using the Diffy::Diff.default_options and Diffy::Diff.default_options= methods. Options passed to Diffy::Diff.new will be merged into the default options.

>> Diffy::Diff.default_options
=> {:diff=>"-U 10000", :source=>"strings", :include_diff_info=>false, :include_plus_and_minus_in_html=>false}
>> Diffy::Diff.default_options.merge!(:source => 'files')
=> {:diff=>"-U 10000", :source=>"files", :include_diff_info=>false, :include_plus_and_minus_in_html=>false}

Custom Formats

Diffy tries to make generating your own custom formatted output easy. Diffy::Diff provides an enumberable interface which lets you iterate over lines in the diff.

>> Diffy::Diff.new("foo\nbar\n", "foo\nbar\nbaz\n").each do |line|
>*   case line
>>   when /^\+/ then puts "line #{line.chomp} added"
>>   when /^-/ then puts "line #{line.chomp} removed"
>>   end
>> end
line +baz added
=> [" foo\n", " bar\n", "+baz\n"]

You can also use Diffy::Diff#each_chunk to iterate each grouping of additions, deletions, and unchanged in a diff.

>> Diffy::Diff.new("foo\nbar\nbang\nbaz\n", "foo\nbar\nbing\nbong\n").each_chunk.to_a
=> [" foo\n bar\n", "-bang\n-baz\n", "+bing\n+bong\n"]

Use #map, #inject, or any of Enumerable's methods. Go crazy.

Ruby Version Compatibility

Support for Ruby 1.8.6 was dropped beggining at version 2.0 in order to support the chainable enumerators available in 1.8.7 and 1.9.

If you want to use Diffy and Ruby 1.8.6 then:

$ gem install diffy -v1.1.0

Report bugs or request features at http://github.com/samg/diffy/issues