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TWiki.ConditionalPluginr1.1 - 11 Aug 2002 - 12:25 - TWikiGuesttopic end

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This is an alpha version and is still under development. See ConditionalPluginDev? for discussion.

This plugin adds the ability to do simple, not nested, conditional rendering in topics.

It attempts to do this in a relatively secure manner by applying the following security measures:

  • restrictive filter for the expression of 'scalar operator scalar'
    • where 'operator' must be one of =,>,<,<,>=,!=,eq,ne,gt,lt,le,ge,<=>,cmp,=~,!~
    • the list of valid operators is hardcoded and cannot be changed by users
    • and 'scalar' is a string consisting of alphanumeric characters + underscore with no whitespace (\w)
  • evaluation of the expression in a sandbox, created with the Safe module.
    • only the opcodes in the :base_core set are allowed (see Opcode)

More sophisticated constructs (like support for range-conditions or nested constructs) may appear in future revisions, if and when the need for them arises.

Syntax Rules

  • !!IF{ scalar operator scalar }% text %ELSE% text %ENDIF%
  • the '%ELSE% text' clause is optional

  • Note: at the moment nested if-else-endif constructs are not supported.


The following example prints something dependent on the topicname (can be usefull in templates)


* This is NOT the WebHome topic

A different approach, without the 'else' clause:

* This is !!IF{ %TOPIC% ne WebHome }% NOT %ENDIF% the WebHome topic

Which of course als results in:

  • This is Good day folks!!

Which results in:

  • Good day folks!!

ConditionalPlugin Global Settings

Plugin settings are stored as preferences variables. To reference a plugin setting write %<plugin>_<setting>%, i.e. %INTERWIKIPLUGIN_SHORTDESCRIPTION%

  • One line description, is shown in the TextFormattingRules topic:
    • Set SHORTDESCRIPTION = Adds conditional rendering (if/then/else)

  • Debug plugin: (See output in data/debug.txt)
    • Set DEBUG = 0

Plugin Installation Instructions

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

  • Download the ZIP file from the Plugin web (see below)
  • Unzip in your twiki installation directory. Content:
    File: Description:
    data/TWiki/ConditionalPlugin.txt Plugin topic
    data/TWiki/ConditionalPlugin.txt,v Plugin topic repository
    lib/TWiki/Plugins/ Plugin Perl module
  • See the examples above to check if the installation was successful.

Plugin Info

Plugin Author: JeroenVanDongen?
Plugin Version: 10 Aug 2002 (V1.000)
Change History:  
10 Aug 2002: Initial version
10 Aug 2002: Improved regexp to deal with multi-line constructs
11 Aug 2002: Added lazy-loading for
CPAN Dependencies: none
Other Dependencies: (part of Perl 5.005_3 and up
Perl Version: 5.005
Plugin Home:

Related Topics: TWikiPreferences, TWikiPlugins

-- JeroenVanDongen? - 10 Aug 2002
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