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
`content_master`	with the current web, this site is the master of the federated sites (see ReadOnlyAndMirrorWebs)
`content_slave`	with the current web, this site is a slave and another site in the federation is the master (see ReadOnlyAndMirrorWebs)
`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; a read-only web puts all topics in this context (see ReadOnlyAndMirrorWebs)
`login` & `logon`	in login / logon script (see TWikiScripts)
`manage`	in manage script (see TWikiScripts)
`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.

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" }%.

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 cannot change TestTopic.
You 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"}%

expands to:
Topic TestTopic does not exist
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
</div>

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

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