# 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|Main/QuerySearch]], with the addition of the following special operators:
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.
$ expands a URL parameter or [[Main/TWikiVariables]] 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 %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: %BR% [[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: %BR% You can 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: %BR% Topic [[TestTopic]] exists Web [[TestTopic]] exists 10. Group membership You %IF{"'%USERNAME%' ingroup 'TWikiAdminGroup'" then="are an admin" else="are a normal user"}% expands to: %BR% You are an admin **Configuration items** are defined in [configure](http://www.dementia.org/twiki/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|Main/TWikiSkins]] 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 [[Main/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 [[Main/TWikiScripts]])
command_line the running script was run from the command line, and not from CGI
diff in rdiff script (see [[Main/TWikiScripts]])
edit in edit script (see [[Main/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 [[Main/TWikiScripts]])
manage in manage script (see [[Main/TWikiScripts]])
mirror if this is a mirror
new_topic if the topic doesn't already exist
oops in oops script (see [[Main/TWikiScripts]])
preview in preview script (see [[Main/TWikiScripts]])
register in register script (see [[Main/TWikiScripts]])
rename in rename script (see [[Main/TWikiScripts]])
resetpasswd in resetpasswd script (see [[Main/TWikiScripts]])
rss if this is an RSS skin rendering
save in save script (see [[Main/TWikiScripts]])
search in search script (see [[Main/TWikiScripts]])
statistics in statistics script (see [[Main/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 [[Main/TWikiScripts]])
view in view script (see [[Main/TWikiScripts]])
viewfile in viewfile script (see [[Main/TWikiScripts]])
rest in rest script (see [[Main/TWikiScripts]])
registration_supported registration is supported by the current [[Main/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]]. Note also that while the [[query syntax|Main/QuerySearch]] 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.