Manual:Checking for page existence

There are several methods to check if a page exists. The table below describes this. But first, here is what each column in the table means:

• Method: The specific technique used to check if a page exists.
• What links here: Indicates if the method impacts the "What links here" page.
• Transclusion: Indicates if the page is counted as transcluded onto another page when this method is applied.
• Limitation: Any limits associated with the method.
• Usage: How the method is typically used.
• Interwiki link: It's applicability to interwiki links.
• Pagename with anchor: Indicates if the method checks the existence of both the page and the specific anchor within the page.

Method	What links here	Transclusion	Limitation	Usage	Interwiki link	Pagename with anchor
#ifexist	yes	no	Expensive (max 100 by default or 500 on Wikimedia wikis)	branching	"doesn't exist"	checks page existence correctly, but not the existence of the anchor
Using #ifeq to compare a transclusion and a link.	yes	yes		branching	"exists"	"exists"
{{PROTECTIONEXPIRY}}	no	no	none	branching	doesn't exist	doesn't exist
linking: class="new" means non-existence	yes	no	none	seeing the page link in a style depending on existence	class="extiw"	checks page existence correctly, but not the existence of the anchor
Special:Allpages	no	no	none	seeing the page listed or not	not listed	n.a.
Special:PrefixIndex	no	no	none	seeing the page listed or not	not listed	n.a.

Examples:

• {{#ifexist:Template:Tc|[[Template:Tc]] exists|[[Template:Tc]] does not exist}} -> >Template:Tc exists
• {{#ifexist:existence a|[[existence a]] exists|[[existence a]] does not exist}} -> existence a does not exist
• Using Manual:Checking for page existence/ifeq method to implement the #ifeq method:
  • {{/ifeq method|Template:Tc}} gives 1
  • {{/ifeq method|Template:Tc|then=[[Template:Tc]] exists|else=[[Template:Tc]] does not exist}} gives Template:Tc exists
  • {{/ifeq method|existence b}} gives 0
  • {{/ifeq method|existence b|then=[[existence b]] exists|else=[[existence b]] does not exist}} gives existence b does not exist
• Using PROTECTIONEXPIRY method:
  • {{/PROTECTIONEXPIRY method|Template:Tc|[[Template:Tc]] exists|[[Template:Tc]] does not exist}} gives Template:Tc exists
  • {{/PROTECTIONEXPIRY method|existence c|''existence c'' exists|''existence c'' does not exist}} gives existence c does not exist
• existence d - this is a redlink, indicating that the page does not exist
• Special:Allpages/existence
• Special:PrefixIndex/exist

{{Special:PrefixIndex/exist}} gives:

• Existing wiki

Another approach involves visiting the specified web address and checking either the content or receiving a message indicating that the page does not exist.

Branching applications

An example of existence detection in practical use is:

• Displaying the content of a webpage if it exists, otherwise showing default content.

A special case is:

• Displaying the content of a webpage if it exists, otherwise displaying nothing.

If there are only a few possible pages, another option is to create them all, with extra pages using default values, and transclude them wherever necessary.

See also

• Help:Extension:ParserFunctions
• Help:What links here
• Help:Transclusion