If Statements < TWiki

The %IF% construct gives TWiki the power to include content in topics based on the value of simple expressions.

%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

Operators
and	True if both sides are true
or	True if one or other side is true
not	negate the following expression
=, !=	String comparison
<, >, <=, >=	Number comparison (there is no explicit numeric =)
context	True if the current context is set (see below)
defined	True if a preference variable or url parameter of this name is defined.
$	expands a URL parameter or TWikiVariable. Plugin handlers are not called. Built-in variables and user-defined preferences are supported. You can pass a limited subset of parameters to TWiki variables by enclosing the variable name in single quotes; for example, `$ 'VARIABLE{value}'`. The quoted string may not contain quotes (' or ").

examples:

%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" }%

Given

Set OPEN_DAY = yes

this expands to:

You are allowed to view 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)
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)
rest	in rest 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.

End of topic
Skip to actions | Back to top

TWiki