1 The `%IF%` construct gives TWiki the power to include content in topics based on the value of simple expressions.
3 `%IF{"CONDITION" then="THEN" else="ELSE"}%`
5 In the example above, if CONDITION evaluates to TRUE, then THEN will be included in the topic; otherwise ELSE will be included.
7 What can be included in the THEN and ELSE parameters is obviously limited by standard TWiki syntax for parameters.
9 The basic syntax of a condition is as follows:
11 expr ::= '(' expr ')' ;
12 expr ::= andexpr | andexpr 'or' expr ;
13 andexpr ::= notexpr | notexpr 'and' andexpr ;
14 notexpr ::= basexpr | 'not' baseexpr ;
15 basexpr ::= atom | uop atom | atom bop basexpr ;
16 uop ::= 'context' | 'defined' | '$' ;
17 bop ::= '=' | '!=' | '>' | '<' | '>=' | '<=' ;
18 atom ::= context identifier, TWiki variable name, single-quoted string, or configuration item
19 <table border="1" cellpadding="0" cellspacing="0">
21 <th bgcolor="#99CCCC" colspan="2"><strong> Operators </strong></th>
25 <td> True if both sides are true </td>
29 <td> True if one or other side is true </td>
33 <td> negate the following expression </td>
37 <td> String comparison </td>
40 <td> <, >, <=, >= </td>
41 <td> Number comparison (there is no explicit numeric =) </td>
45 <td> True if the current context is set (see below) </td>
49 <td> True if a preference variable or url parameter of this name is defined. </td>
53 <td> expands a URL parameter or [[Main/TWikiVariables]]. Plugin handlers <strong>are not called</strong>. Built-in variables and user-defined preferences are supported. You can pass a limited subset of parameters to TWiki variables by enclosing the variable name in single quotes; for example, <code>$ 'VARIABLE{value}'</code>. The <code>'VARIABLE{value}'</code> string may <strong>not</strong> contain quotes (' or "). </td>
59 TWiki variable defined or not
60 %IF{"defined WIKINAME" then="WIKINAME is defined" else="WIKINAME is not defined"}%
62 You are %IF{ "$ WIKINAME='TWikiGuest' and not defined OPEN_DAY" then="not" }% allowed to
63 %IF{ "context view" then="view" else="edit"}% this TWiki today.
66 %IF{ "defined search" then="Search: %URLPARAM{search}%" else="No search passed in"}%
68 Configuration item set or not
69 %IF{ "{AntiSpam}{HideUserDetails}" then="User details are hidden" }%
71 url param t is %IF{ "0 < $ t and $ t < 1000" then="in" else="out of"}% range.
74 %IF{ "$'URLPARAM{scope}'='text'" then="Plain text search" }%
76 **Configuration items** are defined in `configure`. You cannot see the value of a configuration item, you can only see if the item is set or not.
78 **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:
80 <table border="1" cellpadding="0" cellspacing="0">
82 <th bgcolor="#99CCCC"><strong> id </strong></th>
83 <th bgcolor="#99CCCC"><strong> context </strong></th>
86 <td> absolute_urls </td>
87 <td> Set if absolute URLs are required </td>
90 <td> authenticated </td>
91 <td> a user is authenticated </td>
95 <td> when the body text is being processed in a view (useful in plugin handlers) </td>
99 <td> current environment supports login </td>
103 <td> in changes script (see [[Main/TWikiScripts]]) </td>
106 <td> command_line </td>
107 <td> the running script was run from the command line, and not from CGI </td>
111 <td> in rdiff script (see [[Main/TWikiScripts]]) </td>
115 <td> in edit script (see [[Main/TWikiScripts]]) </td>
118 <td> footer_text </td>
119 <td> when the footer text is being processed in a view (useful in plugin handlers) </td>
122 <td> header_text </td>
123 <td> when the header text is being processed in a view (useful in plugin handlers) </td>
126 <td> i18n_enabled </td>
127 <td> when user interface [[Main/I18N]] support is enabled (i.e., user can choose the language for UI) </td>
131 <td> if active links such as 'edit' and 'attach' should be disabled </td>
135 <td> if this is a mirror </td>
139 <td> if the topic doesn't already exist </td>
143 <td> in oops script (see [[Main/TWikiScripts]]) </td>
147 <td> in preview script (see [[Main/TWikiScripts]]) </td>
151 <td> if this is an RSS skin rendering </td>
155 <td> in save script (see [[Main/TWikiScripts]]) </td>
159 <td> in search script (see [[Main/TWikiScripts]]) </td>
163 <td> in view script (see [[Main/TWikiScripts]]) </td>
167 <td> in rest script (see [[Main/TWikiScripts]]) </td>
171 In addition there is a context identifier for each enabled plugin; for example, if `GallousBreeksPlugin` is installed **and enabled**, then the context ID `GallousBreeksPluginEnabled` will be set. Other extensions may set additional context identifiers.
173 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]].