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ALERT! NOTE: This is a DistributionDocument. Please help maintain high quality documentation: This is a wiki, please fix the documentation if you find errors or incomplete content. Put questions and suggestions concerning the documentation of this topic in the comments section below. Use the Support web for problems you are having using TWiki.

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:

context True if the current context is set (see below)
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'. 'X' can be a login name or a wikiname.
defined True if a preference variable or url parameter of this name is defined.
isempty True if a preference variable, url parameter or session variable of this name has an empty value. It is equivalent to the expression (defined(x) || $x='')
$ 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}

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:

id context
absolute_urls Set if absolute URLs are required
attach in attach script (see TWikiScripts)
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
login & logon in login / logon script (see TWikiScripts)
manage in manage script (see TWikiScripts)
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)
register in register script (see TWikiScripts)
rename in rename script (see TWikiScripts)
resetpasswd in resetpasswd script (see TWikiScripts)
rss if this is an RSS skin rendering
save in save script (see TWikiScripts)
search in search script (see TWikiScripts)
statistics in statistics script (see TWikiScripts)
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.
upload in upload script (see TWikiScripts)
view in view script (see TWikiScripts)
viewfile in viewfile script (see TWikiScripts)
rest in rest script (see TWikiScripts)
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 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.


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" }%.
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 can change this topic.
You can change TestTopic.
You can 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"}%
expands to:
Topic TestTopic exists
Web Sandbox 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

11. Conditional include

%IF{"'%USERNAME%' ingroup 'ExecutiveGroup'" then="$percntINCLUDE{ExecutiveReport}$percnt"}% 
The ExecutiveReport topic is only included if the user is in the ExecutiveGroup.

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
Above text is only shown to users who are in the TWikiAdminGroup.

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

Comments & Questions about this Distribution Document Topic

Greetings! I've been pulling my hair out for 6 hours trying to solve an issue, and finally got it. It has to do with conditional setting of variables.

Here's my code, the goal being to define a value for LFS based on either a URL parameter or a session variable:

   * Set PARAM_OFFERED = %IF{ "$'URLPARAM{locationfeatureset}'=''" then="false" else="true" }%
   * Set PARAM_VALUE= 
   * Set SESSION_OFFERED = %IF{ "$'SESSION_VARIABLE{locationfeatureset}'=''" then="false" else="true" }%
   * Set SESSION_VALUE = %SESSION_VARIABLE{"locationfeatureset"}%


   * Set LFS_DEFAULT = %IF{ "%SESSION_OFFERED%=true" then="%SESSION_VALUE%" else="on" }%
   * Set LFS = %IF{ "%PARAM_OFFERED%=true" then="%PARAM_VALUE%" else="%LFS_DEFAULT%" }%

The error was I was using LSF in the place of LFS_DEFAULT. By having setting a variable and having the return be one of the variables, it causes messy loops:

   * Set VAR = %IF{ "1=1" then="%VAR% else="false" }%

Would you make a comment in the IfStatements topic that you shouldn't do such setting? thanks! Ken

-- KenBonninJr - 08 Nov 2006

The IF can be a bit complex. In fact, I do not understand what you are trying to document. Could you give it a try? Simply edit the main document part on top.

-- PeterThoeny - 12 Nov 2006

It seems I can't use an %IF{} inside of WebLeftBar. When I view WebLeftBar directly, my %IF{} statement works. But when viewing the Web itself, I see the first part of the %IF{} statement itself on the LeftBar.

-- MarkKeisler - 25 Jan 2007

This looks like a Support question, possibly a %TOPIC% vs. %BASETOPIC% issue.

-- PeterThoeny - 27 Jan 2007

Can I use this to detect if some plugin is enabled/installed?

-- MikkoLaakso - 30 Jun 2007

Found it, added examples.

-- MikkoLaakso - 30 Jun 2007

I could not make the example 3 work in my TWiki 4.1.2:

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

Test: give the parameter "search" in url (url + ?search=something): No search passed in

Seems like $percnt does not expand? This means I cannot use conditionals to give additional functionality, if a plugin is on.

-- MikkoLaakso - 15 Jul 2007

I'm going mad trying to get something to work. See Support.QueryByAuthor for details

The following condition fails. The results show that the condition should NOT fail; most of the results were created, or modified, by me. Nevertheless, the condition fails consistently.

What am I doing wrong?

%SEARCH{"." scope="topic" regex="on" nonoise="on" limit="100" format="$percntIF{\"$ wikiname=VickiBrown or $createwikiname=VickiBrown\" then=\"|YES| [[$topic]] | $createwikiusername | $wikiusername |\" else=\"|NO| [[$topic]] |  $createwikiname |  $wikiname |\"}$percnt"     }% 

-- VickiBrown - 22 Jul 2007

Apparently what I was doing wrong was the space after the $... even though all of the examples for %IF insert a space after the $

-- VickiBrown - 22 Jul 2007

Even though it says plugin handlers are not called and only URL parameters, standard TWiki variables or preference variables are supported, I was still able to get an IF statement to work that evaluated a Workflow plugin variable %WORKFLOWSTATE%. Is this a fluke or has the IF variable been modified to allow for plugin variables?

-- GarySprague - 27 Jun 2008

REMARK: IF is in capital, than and else are not!

-- Emiel Van Riel - 2017-10-26

Please use the Support forum if you have questions about TWiki features. This comment section is about the documentation of this topic.
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Topic revision: r21 - 2017-10-26 - EmielVanRiel
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