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:
%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 [[Main/TWikiVariables]]. 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 edit this TWiki today.
Context identifiers are used in TWiki to label various stages of the rendering process. They are especially useful for [[skin|Main/TWikiSkins]] 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 [[Main/TWikiScripts]]) |
command_line |
the running script was run from the command line, and not from CGI |
diff |
in rdiff script (see [[Main/TWikiScripts]]) |
edit |
in edit script (see [[Main/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 [[Main/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 [[Main/TWikiScripts]]) |
preview |
in preview script (see [[Main/TWikiScripts]]) |
rss |
if this is an RSS skin rendering |
save |
in save script (see [[Main/TWikiScripts]]) |
search |
in search script (see [[Main/TWikiScripts]]) |
view |
in view script (see [[Main/TWikiScripts]]) |
rest |
in rest script (see [[Main/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]].