In addition, the following special operators are supported:

You can test if a context identifier is set or not, using conditions such as "context authenticated". Context identifier are used in TWiki to label various stages of the rendering process. They are especially useful for skin authors to find out where they are in the rendering process. The following context identifiers are available:

In addition there is a context identifier for each enabled plugin; for example, if GallousTwistyPlugin is installed and enabled, then the context ID GallousTwistyPluginEnabled will be set. Other extensions may set additional context identifiers.

The %IF{}% statement is deliberately kept simple. In particular, note that there is no way to conditionally execute a Set statement. If you need more sophisticated control over formatting, then consider using the SpreadSheetPlugin.

Note also that while the query syntax can be used to access form fields, there are some contexts in which an IF statement may be used where there is no topic context, or the topic context is not what you expected.

Examples

1. TWiki variable defined or not

%IF{"'%USERNAME%' ingroup 'ExecutiveGroup'" then="$percntINCLUDE{ExecutiveReport}$percnt"}% 

12. Hide section of text conditionally using CSS display

<div style="visibility: %IF{"'%USERNAME%' ingroup 'TWikiAdminGroup'" then="visible" else="hidden"}%">
   * Conditional text enclosed in div tags here...
   * ...can be as long as needed
</div>

-- Contributors: TWiki:Main/ArthurClemens, TWiki:Main/CrawfordCurrie, TWiki:Main/PeterThoeny, TWiki:Main/SopanShewale, TWiki:Main/SvenDowideit, TWiki:Main/WillNorris - 2010-04-09

IF Statements

The basic syntax of a condition is the same as the syntax used for queries, with the addition of the following special operators:

Examples:

1. TWiki variable defined or not

%IF{ "defined search" then="Search: $percntURLPARAM{search}$percnt" else="No search passed in"}%

%IF{ "{AntiSpam}{HideUserDetails}" then="User details are hidden" }%

7. Plugin enabled test

TablePlugin is %IF{ "context TablePluginEnabled" then="enabled" else="disabled" }%.

8. Check access permissions

You %IF{"'%TOPIC%' allows 'change'" then="can" else="cannot"}% change this topic.
You %IF{"'Sandbox.TestTopic' allows 'change'" then="can" else="cannot"}% change Sandbox.TestTopic.
You %IF{"'Sandbox' allows 'change'" then="can" else="cannot"}% change Sandbox web

9. Check topic existance

Topic Sandbox.TestTopic %IF{"istopic 'Sandbox.TestTopic'" then="exists" else="does not exist"}%
Web Sandbox.TestTopic %IF{"isweb 'Sandbox'" then="exists" else="does not exist"}%

10. Group membership

You %IF{"'%USERNAME%' ingroup 'TWikiAdminGroup'" then="are an admin" else="are a normal user"}% 

IF Statements

%IF{"CONDITION" then="THEN" else="ELSE"}%

In the example above, if CONDITION evaluates to TRUE, then THEN will be included in the topic; otherwise ELSE will be included.

What can be included in the THEN and ELSE parameters is obviously limited by standard TWiki syntax for parameters. The best way to use this feature is to define two TWikiVariables, one for the THEN case and the other for the ELSE case. For example:

<!--
   * Set LI = Fred is here!
   * Set LO = Fred is there!
-->
%IF{"context authenticated and defined WIKINAME and $ WIKINAME='FredBloggs'" then="%LI%" else="%LO%"}%

The basic syntax of a condition is as follows:

expr ::= '(' expr ')' ;
expr ::= andexpr | andexpr 'or' expr ;
andexpr ::= notexpr | notexpr 'and' andexpr ;
notexpr ::= basexpr | 'not' baseexpr ;
basexpr ::= atom | uop atom | atom bop basexpr ;
uop ::= 'context' | 'defined' | '$' ;
bop ::= '=' | '!=' | '>' | '<' | '>=' | '<=' ;
atom ::= context identifier, TWiki variable name, single-quoted string

%IF{"defined WIKINAME" then="WIKINAME is defined" else="WIKINAME is not defined"}%

You are %IF{ "$ WIKINAME='TWikiGuest' and not defined OPEN_DAY" then="not" }% allowed to
%IF{ "context view" then="view" else="edit"}% this TWiki today.

%IF{ "defined search" then="Search: %URLPARAM{search}%" else="No search passed in"}%

url param t is %IF{ "0 < $ t and $ t < 1000" then="in" else="out of"}% range.

%IF{ "$'URLPARAM{scope}'='text'" then="Plain text search" }% 

• Set OPEN_DAY = yes

You are not allowed to edit this TWiki today.

Context identifiers are used in TWiki to label various stages of the rendering process. They are especially useful for skin authors to find out where they are in the rendering process. The following context identifiers are available:

id <-- -->	context
absolute_urls	Set if absolute URLs are required
authenticated	a user is authenticated
body_text	when the body text is being processed in a view (useful in plugin handlers)
can_login	current environment supports login
changes	in changes script (see TWikiScripts)
command_line	the running script was run from the command line, and not from CGI
diff	in rdiff script (see TWikiScripts)
edit	in edit script (see TWikiScripts)
footer_text	when the footer text is being processed in a view (useful in plugin handlers)
header_text	when the header text is being processed in a view (useful in plugin handlers)
i18n_enabled	when user interface I18N support is enabled (i.e., user can choose the language for UI)
inactive	if active links such as 'edit' and 'attach' should be disabled
mirror	if this is a mirror
new_topic	if the topic doesn't already exist
oops	in oops script (see TWikiScripts)
preview	in preview script (see TWikiScripts)
rest	in rest script (see TWikiScripts)
rss	if this is an RSS skin rendering
save	in save script (see TWikiScripts)
search	in search script (see TWikiScripts)
view	in view script (see TWikiScripts)

In addition there is an identifier for each enabled plugin; for example, if GallousBreeksPlugin is installed and enabled, then the context ID GallousBreeksPluginEnabled will be set.

The %IF% statement is deliberately kept simple. In particular, note that there is no way to conditionally execute a Set statement. If you need more sophisticated control over formatting, then consider using the SpreadSheetPlugin.