Compare Revisions Add-On

This add-on compares the renderd HTML output of two revisions and shows the differences broken down to the word-by-word level if necessary. The output can be formatted by templates and skins.


The CompareRevisionsAddOn compares two revisions of a document, like rdiff does. But in contrast to normal rdiff, the comparison is done with the rendered HTML output of the revisions instead of the Foswiki source text files. (This feature was proposed by many of our users, who found the normal rdiff output too technical - even with the sidebyside option - and wanted to see differences in the content of the page).

Furthermore, the differences between the revisions are shown as close as possible. If necessary, this means that different words are marked instead of whole lines or even paragraphs.

The differences may be shown in two formats, either side-by-side or as an interwoven output of the old and new revision (like it is done in Word or StarOffice/!OpenOffice):

  • Screenshot of interwoven output:

  • Screenshot of side-by-side output:

These screenshots have been taken from CompareRevisionsAddOnDemoTopic.

The appearance can be affected by templates and skins.


Call http://your/twiki/bin/compare/Web/Topic?parameters from your browser


rev1=rev and rev2=rev
Revision numbers of the two revisions which should be compared. Defaults to the last two revisions. (More exact: rev2 defaults to the latest edition, rev1 defaults to rev2 - 1)

render=interweave or render=sidebyside
Chooses the output format. May also be given in the preference variable COMPARERENDERSTYLE

The number n of unchanged sections which should be shown around changed sections. A section means a top-level section like a paragraph, table, etc. If n=-1 (the default), all unchanged sections are shown. May also be given in the preference variable COMPARECONTEXT

Chooses someskin for the output. See section Templates below


The output of the script is rendered by templates. Two templates are needed, compare.tmpl (or for the side-by-side format, and interweave.tmpl (or for the interwoven format.

The templates itself are broken into 7 parts

template for start of page
template for unchanged section 
which is not printed according to context
template for unchanged section 
which is printed
template for changed section
template for added section
template for deleted section
template for end of page

All empty templates for a section default to their predecessor. (E.g. if you do not specify a template for a deleted section, it defaults to the template for an added section, which in turn may default to the template for a changed section).

In the templates for a section, %TEXT1% is replaced by the text of the old revision and %TEXT2% is replaced by the text of the new revision. In interwoven output, only %TEXT1% is used.

Examples for templates can be found in the default template files from the distribution (compare.tmpl, compare.pattern.tmpl, interweave.tmpl, interweave.pattern.tmpl ).

CSS Styles

The differences in the two revisions are marked with the help of CSS style classes, whose appearance should be defined in the templates.

The following classes are used:

Class for added items (i.e. items which are in the newer revision, but not yet in the older one)

Class for deleted items (i.e. items which are in the older revision, but no more in the newer one)

Class for the items from the older revision which have been changed.

Class for the items from the newer revision which have been changed.

In the default templates files from the distribution, the classes twikiCompareAdd and twikiCompareChange1 are defined with a light red background and stroken out text, and twikiCompareDelete and twikiCompareChange2 are defined with a light green background.

Add-On Installation Instructions

Note: You do not need to install anything on the browser to use this add-on. The following instructions are for the administrator who installs the add-on on the server where Foswiki is running.

  • This script needs some additional Perl modules. If necessary, download and install the required perl modules from CPAN. If you do not want to install these modules in your standard perl location, install them in /your/twiki/lib. (See e.g. perldoc perlmodinstall on how to install perl modules).
    These modules are required:
    • HTML::Tree (with HTML::TreeBuilder and HTML::Element). These modules in turn need
    • Algorithm::Diff (which is included in the standard Foswiki installation
  • Download the ZIP file from the Add-on Home (see below)
  • Unzip in your twiki installation directory. Content:
    File: Description:
    data/System/CompareRevisionsAddOn.txt Add-on topic
    bin/compare Add-on script
    lib/Foswiki/UI/ Perl package used by the script
    templates/compare.tmpl Template for side-by-side output
    templates/compare.pattern.tmpl Same for pattern skin
    templates/interweave.tmpl Template for interwoven output
    templates/interweave.pattern.tmpl Same for pattern skin
    lib/Foswiki/Plugins/ Helper plugin
    data/System/CompareRevisionsAddonPlugin.txt Plugin topic
    pub/System/CompareRevisionsAddOn/interweaved.png Interwoven screenshot
    pub/System/CompareRevisionsAddOn/sidebyside.png Side-by-side screenshot
    data/Sandbox/CompareRevisionsAddOnDemoTopic.txt Demonstration topic
    data/Sandbox/CompareRevisionsAddOnDemoTopic.txt,v Demonstration topic history

  • Test if the installation was successful:
    Call %SCRIPTURL%/compare/Web/Topic with some existing topic. (Try for instance CompareRevisionsAddOnDemoTopic and compare your output with above screenshots).

  • Enable the helper plugin CompareRevisionsAddonPlugin with the configure script
  • This plugin will support the HistoryPlugin, if it is enabled
  • If you disable this plugin, the skin will behave like standard PatternSkin again

Add-On Info

Plugin Author: Foswiki:Main.KennethLavrsen
Copyright ©: 2006, JChristophFuchs; 2008 Kenneth Lavrsen and Foswiki Contributors
License: GPL (GNU General Public License)
Version: 4995 (2009-09-19)
Release: 2009-09-19
Change History:  
19 Sep 2009 Kenneth Lavrsen: Expert settings in plugins makes configure fail to save. Using the hidden (H) setting instead which is much better anyway as this is not a setting to be altered by a user.
18 Sep 2009 Kenneth Lavrsen: Expert settings in plugins makes configure fail to save. Settings therefore un-experted again
12 Sep 2009 Kenneth Lavrsen: Fixed problem with tables always showing up as changed even when they were not
09 Aug 2009 Plugin is now a default plugin shipped with Foswiki. It will later have its function integrated in core in a future Foswiki version so its life as default plugin is temporary. Changed its switchboard setting to EXPERT so it is hidden in configure. You should never need to change this anyway.
22 Mar 2009 Gilmar Santos Jr: ported to FSA architecture (Foswiki:Tasks/Item1352)
09 Jan 2009 Gilmar Santos Jr: fixed ambigous print (Foswiki:Tasks.Item716)
08 Dec 2008 Kenneth Lavrsen: Changed the author to myself. JChristophFuchs is the original author but announced in 2006 that he no longer maintains this plugin. So now I officially take the task as maintainer. Plugin is changed to Foswiki namespace and tested and works under Foswiki 1.0.0. Policy is now feel free to modify but please do not break compatibility.
07 Nov 2007 Arthur Clemens: Updated for TWiki 4.2
09 Apr 2006 Updated for new PatternSkin in TWikiRelease04x00x02
26 Feb 2006 Updated for TWiki 4
02 Mar 2005 Corrected bug concerning uninitialized elements
03 Feb 2005 Removed blank paragraphs before comparing
20 Jan 2005 Initial version
CPAN Dependencies: HTML::Parser, HTML::Tagset, HTML::Tree
Other Dependencies: none
Perl Version: 5.008
Add-on Home:

Related Topic: ContributedAddOns

Topic attachments
I Attachment Action Size Date Who Comment
pngpng interweave.png manage 23.5 K 2009-09-19 - 07:24 AdminUser Saved by install script
pngpng sidebyside.png manage 34.3 K 2009-09-19 - 07:24 AdminUser Saved by install script
Topic revision: r2 - 2010-02-10 - 20:39:27 - AdminUser
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