Conditional Plugin

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{ operator="1" scalar="1" }: %PARAM4%
text %ELSE% text %ENDIF%

• the '%ELSE% text' clause is optional

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

Examples

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

IF{ "%TOPIC% eq WebHome" }: Bad expression at %TOPIC% eq WebHome
This is the WebHome topic %ELSE% This is NOT the WebHome topic %ENDIF%

Result

IF{ ConditionalPlugin="1" WebHome="1" eq="1" }: Bad expression at %TOPIC% eq WebHome
This is the WebHome topic %ELSE% This is NOT the WebHome topic %ENDIF%

A different approach, without the 'else' clause:

• This is

IF{ "%TOPIC% ne WebHome" }: Bad expression at %TOPIC% ne WebHome
NOT %ENDIF% the WebHome topic

Which of course als results in:

• This is

IF{ ConditionalPlugin="1" WebHome="1" ne="1" }: Bad expression at %TOPIC% ne WebHome
NOT %ENDIF% the WebHome topic

Or:

IF{ "%GMTIME{\"$hour\"" }: Bad expression at %GMTIME{"$hour"
> 18 }% Good evening folks!! %ELSE% Good day folks!! %ENDIF%

Which results in:

• Good evening folks!! %ELSE% Good day folks!! %ENDIF%

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 ConditionalPlugin.zip 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/ConditionalPlugin.pm	Plugin Perl module

• See the examples above to check if the installation was successful.

Plugin Info

Related Topics: TWikiPreferences, TWikiPlugins

-- JeroenVanDongen - 10 Aug 2002

Because this plugin is used, but does not appear to be maintained, I have switched the CVS modification policy. If you have a problem with this, switch it back. -- CrawfordCurrie - 03 Apr 2004