IF Statements

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 shown in the topic; otherwise ELSE will be shown.

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 such as $percnt for % 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 operators =, !=, ~, <, >, <=, >=, NOT, AND, OR, (), and functions lc(), uc(), d2n().

In addition, the following special operators are supported:

You can test if a configuration item is set or not, using conditions such as "{AntiSpam}{HideUserDetails}". It is not possible see the value of a configuration. Configuration items are defined in configure.

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

2. Compare TWiki variable

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

3. URL parameter

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

4. Range test on URL parameter

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

5. Text comparison of URL parameter

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

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" }%.

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 existence

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

11. Conditional include

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

12. Hide section of text conditionally using CSS display

<div style="display: %IF{"'%USERNAME%' ingroup 'TWikiAdminGroup'" then="block" else="none"}%">
   * Conditional text enclosed in div tags here...
   * ...can be as long as needed
</div>

Related Topics: QuerySearch, VarIF, VarGET, VarSET, VarSEARCH, FormattedSearch, FormatTokens, SpreadSheetPlugin, TWikiScripts

-- Contributors: TWiki:Main.ArthurClemens, TWiki:Main.CrawfordCurrie, TWiki:Main.PeterThoeny, TWiki:Main.SopanShewale, TWiki:Main.SvenDowideit, TWiki:Main.WillNorris - 2012-08-07

IF Statements

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"}%

%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: $percntURLPARAM{search}$percnt" 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" }% 

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

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

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

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

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

• Conditional text enclosed in div tags here...
• ...can be as long as needed

IF Statements

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.

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 operators =, !=, ~, <, >, <=, >=, NOT, AND, OR, (), and functions lc(), uc(), d2n(). In addition, the following special operators are supported:

Examples:

1. TWiki variable defined or not

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

2. Compare TWiki variable

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

3. URL parameter

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

4. Range test on URL parameter

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

5. Text comparison of URL parameter

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

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" }%.

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"}% 

11. Hide section of text conditionally using CSS visibility

<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>

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:

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.

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.

IF Statements

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.

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 operators =, !=, ~, <, >, <=, >=, NOT, AND, OR, (), and functions lc(), uc(), d2n(). In addition, the following special operators are supported:

Examples:

1. TWiki variable defined or not

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

2. Compare TWiki variable

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

3. URL parameter

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

4. Range test on URL parameter

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

5. Text comparison of URL parameter

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

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" }%.

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"}% 

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:

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.

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.

IF Statements

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.

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.

1. TWiki variable defined or not

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

2. Compare TWiki variable

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

3. URL parameter

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

4. Range test on URL parameter

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

5. Text comparison of URL parameter

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

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" }%.

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"}% 

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:

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.

IF Statements

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.

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:

Examples:

1. TWiki variable defined or not

2. Compare TWiki variable

3. URL parameter

4. Range test on URL parameter

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

5. Text comparison of URL parameter

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

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" }%.

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"}% 

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:

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.

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.

%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.

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:

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.

IF Statements

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 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

TWiki variable defined or not
%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.

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

Configuration item set or not
%IF{ "{AntiSpam}{HideUserDetails}" then="User details are hidden" }%

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

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

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:

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.

%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 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

TWiki variable defined or not
%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.

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

Configuration item set or not
%IF{ "{AntiSpam}{HideUserDetails}" then="User details are hidden" }%

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

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

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.

%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.

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 ::= '=' | '!=' | '>' | '<' | '>=' | '<=' ;

You are not allowed to edit this TWiki today.

%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:

<!--

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" }% 

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:

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.

%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:

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.