Difference: IfStatements (5 vs. 6)

Revision 607 Jul 2007 - Main.TWikiContributor

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IF Statements

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IF Statements

  The %IF% construct gives TWiki the power to include content in topics based on the value of simple expressions.
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  In the example above, if CONDITION evaluates to TRUE, then THEN will be included in the topic; otherwise ELSE will be included.
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What can be included in the THEN and ELSE parameters is obviously limited by standard TWiki syntax for parameters.
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Note that because of the way TWiki evaluates, then whatever is in the THEN and ELSE parameters will already have been expanded by the time the condition is actually evaluated. The standard FormatTokens can be used in the THEN and ELSE parameters when you need to delay evaluation of (for example) a TWiki variable.

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

 
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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, or configuration item
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)
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allows 'X' allows 'Y' is true if web/topic 'X' exists and allows access mode 'Y' for the current user. Web access rights are only checked if there is no topic called 'X'.
istopic istopic 'X' is true if topic 'X' exists
isweb isweb 'X' is true if web 'X' exists
ingroup 'X' ingroup 'Y' is true if user 'X' is in group 'Y'
 
defined True if a preference variable or url parameter of this name is defined.
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$ 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 'VARIABLE{value}' string may not contain quotes (' or ").
examples:
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$ expands a URL parameter or TWikiVariable name. 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 'VARIABLE{value}' string may not contain quotes (' or ").
{X} expands to the value of the configuration variable {X} - for example, {ScriptUrlPath}

Examples:

1. TWiki variable defined or not

 
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TWiki variable defined or not
 WIKINAME is defined
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2. Compare TWiki variable
 You are not allowed to edit this TWiki today.
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URL parameter No search passed in

Configuration item set or not User details are hidden

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3. URL parameter
%IF{ "defined search" then="Search: $percntURLPARAM{search}$percnt" else="No search passed in"}%
 
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4. Range test on URL parameter
 url param t is

IF{ "0 < $ t and $ t < 1000" else="out of" then="in" }: Syntax error in '0 < $ t and $ t < 1000' at ' t and $ t < 1000' range.

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Text comparison
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5. Text comparison of URL parameter
 
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6. Configuration item set or not
%IF{ "{AntiSpam}{HideUserDetails}" then="User details are hidden" }%

7. Plugin enabled test

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

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
expands to:
You cannot change this topic. You can change TestTopic? . You can 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"}%
expands to:
Topic TestTopic? does not exist Web TestTopic? exists

10. Group membership

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

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:

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rss if this is an RSS skin rendering
save in save script (see TWikiScripts)
search in search script (see TWikiScripts)
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textareas_hijacked provided for use by editors that highjack textareas, and want to signal this fact. This is used by skins, for example, so they can suppress extra controls when textareas have been hijacked.
 
view in view script (see TWikiScripts)
rest in rest script (see TWikiScripts)
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registration_supported registration is supported by the current UserMapper?
registration_enabled set if {Register}{EnableNewUserRegistration} is on, and registrationis supported
passwords_modifyable set if the password manager support changing the password / email
  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.

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.

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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.
 
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