Help:Page existence

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{{H:h {{#if: Help|Help|Help}}||enname=}}

Contents 1 Branching applications 2 CSS class 3 Notes 4 See also

Wikitext methods to determine whether a page exists:

method	what links here [1]	transclusion [1]	limitation	usage	interwiki link[1]	pagename with anchor
#ifexist	yes	no[1]	not more than now 500 on a page[1]	branching	"does not exist"	checks page existence correctly, but not the existence of the anchor
[[{{#if:|template}}:{{#if:|exists|template}}:{{#if:|foo|exists}}]]}} ( {{#if:1|[[{{#if:|template}}:{{#if:|exists|template}} talk:{{#if:|foo|exists}}|talk]]}} {{#if:1|[{{fullurl:{{#if:|template}}:{{#if:|exists|template}}:{{#if:|foo|exists}}|action=edit}} edit]}} {{#if:|[{{fullurl:{{#if:|template}}:{{#if:|exists|template}}:{{#if:|foo|exists}}|action=watch}} watch]}} {{#if:|{{#ifeq:{{#if:|exists|template}}|user|[[{{#if:|template}}:Special:Contributions/{{#titleparts:{{#if:|foo|exists}}|1}}|contribs]]}}}} {{#if:1|[{{fullurl:{{#if:|template}}:{{#if:|exists|template}}:{{#if:|foo|exists}}|action=history}} history]}} {{#if:1|[{{fullurl:{{#if:|template}}:Special:Whatlinkshere/{{#if:|exists|template}}:{{#if:|foo|exists}}|limit=1000}} links]}} {{#if:|[{{fullurl:{{#if:|template}}:Special:Log|page=%7B%7B%23if%3A%7Cexists%7Ctemplate%7D%7D%3A%7B%7B%23if%3A%7Cfoo%7Cexists%7D%7D}} logs]}} {{#if:|[[{{#if:|template}}:Special:Prefixindex/{{#if:|exists|template}}:{{#if:|foo|exists}}|localspace]]}} {{#if:|[{{fullurl:{{#if:|template}}:{{#if:|exists|template}}:{{#if:|foo|exists}}|action=delete}} delete]}} {{#if:|{{#ifeq:{{#if:|exists|template}}|user|[[{{#if:|template}}:Special:Blockip/{{#titleparts:{{#if:|foo|exists}}|1}}|block]]}}}} ), where care is taken that the comparison is insensitive to the applicable conversions	yes	yes		branching	"exists"	"exists"
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:

• {{p{{#ifeq:eq|eq|1|2}}|{{p{{#ifeq:+|-|1|2}}|{&#{{#if:|123;[[Template:#ifexist:existence a|#ifexist:existence a]]|123;#ifexist:existence a}}|1|0|{{{4}}}}} gives {{#ifexist:existence a|1|0|{{{4}}}}} [1]|{{p{{#ifeq:eq|eq|1|2}}|{{p{{#ifeq:0|0|1|2}}|"{&#{{#if:|123;[[Template:#ifexist:existence a|#ifexist:existence a]]|123;#ifexist:existence a}}|1|0}}" gives "{{#ifexist:existence a|1|0}}" [2]|{{p{{#ifeq:eq|eq|1|2}}|{{p{{#ifeq:1|1|1|2}}|"{{{{#if:|{{#ifeq:{{Template:#ifexist:existence a}}|{{#ifexist:existence a}}|[[Template:#ifexist:existence a|#ifexist:existence a]]|#ifexist:existence a}}|#ifexist:existence a}}|{{#switch:p{{#switch:p1q|p q=&s|p

q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}q|p

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|&*=*|&#=#|&:=:}}{{ {{#switch:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|{|&p|}|&e|&s|&nl|&*|&#|&:|*|**|***|#|##|###|:|::|:::|;=void|1x}}|{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}}}{{#switch:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|*=*|**=**|***=***|#=#|##=##|###=###|:=:|::=::|:::=:::|;=;}}{{ {{#switch:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|&s=1x|void}}| }}{{#ifeq:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|&|amp;}}}}" gives "{{#ifexist:existence a|1}}" [http://sdnhq.undp.org/w/index.php?title=Special:ExpandTemplates&input=%22%7B%7B%23ifexist%3Aexistence+a%7c{{#switch:p{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}q|p

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q=%0d}}{{#switch:{{#switch:p1q|p q=&s|p

q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|&p=%7c|&e=%3d|&s=+|&nl=%0d|&*=%2a|&#=%23|&:=%3a|%7B%7B%23switch%3Ap1q%7Cp+q%3D%26s%7Cp%0Aq%3D%26nl%7Cp%2Aq%3D%26%2A%7Cp%23q%3D%26%23%7Cp%3Aq%3D%26%3A%7C1%7D%7D}}%7D%7D%22]|"{{{{#if:|{{#ifeq:{{Template:#ifexist:existence a}}|{{#ifexist:existence a}}|[[Template:#ifexist:existence a|#ifexist:existence a]]|#ifexist:existence a}}|#ifexist:existence a}}}}" gives "{{#ifexist:existence a}}" {{#ifeq:gives||||||}} [3]}}|{{p{{#ifeq:1|1|2}}|1|"{{{{#if:|{{#ifeq:{{Template:#ifexist:existence a}}|{{#ifexist:existence a}}|[[Template:#ifexist:existence a|#ifexist:existence a]]|#ifexist:existence a}}|#ifexist:existence a}}|{{#switch:p{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}q|p

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|&*=*|&#=#|&:=:}}{{ {{#switch:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|{|&p|}|&e|&s|&nl|&*|&#|&:|*|**|***|#|##|###|:|::|:::|;=void|1x}}|{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}}}{{#switch:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|*=*|**=**|***=***|#=#|##=##|###=###|:=:|::=::|:::=:::|;=;}}{{ {{#switch:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|&s=1x|void}}| }}{{#ifeq:{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|&|amp;}}}}" gives "{{#ifexist:existence a|1}}" [http://sdnhq.undp.org/w/index.php?title=Special:ExpandTemplates&input=%22%7B%7B%23ifexist%3Aexistence+a%7c{{#switch:p{{#switch:p1q|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}q|p

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q=%0d}}{{#switch:{{#switch:p1q|p q=&s|p

q=&nl|p*q=&*|p#q=&#|p:q=&:|1}}|&p=%7c|&e=%3d|&s=+|&nl=%0d|&*=%2a|&#=%23|&:=%3a|%7B%7B%23switch%3Ap1q%7Cp+q%3D%26s%7Cp%0Aq%3D%26nl%7Cp%2Aq%3D%26%2A%7Cp%23q%3D%26%23%7Cp%3Aq%3D%26%3A%7C1%7D%7D}}%7D%7D%22]}}}}}}|{{p{{#ifeq:0|1|2}}|0|"{&#{{#if:|123;[[Template:#ifexist:existence a|#ifexist:existence a]]|123;#ifexist:existence a}}|1|0}}" gives "{{#ifexist:existence a|1|0}}" [4]}}}}}}|{{p{{#ifeq:+|1|2}}|-|{&#{{#if:|123;[[Template:#ifexist:existence a|#ifexist:existence a]]|123;#ifexist:existence a}}|1|0|{{{4}}}}} gives {{#ifexist:existence a|1|0|{{{4}}}}} [5]}}}}

• {{p{{#ifeq:eq|eq|1|2}}|{{p{{#ifeq:0|0|1|2}}|{&#{{#if:|123;exists|123;exists}}|existence b|1|0}} gives Template:Exists [6]|{{p{{#ifeq:eq|eq|1|2}}|{{p{{#ifeq:1|1|1|2}}|"{&#{{#if:|123;exists|123;exists}}|existence b|1}}" gives "Template:Exists" [7]|{{p{{#ifeq:eq|eq|1|2}}|{{p{{#ifeq:existence b|existence b|1|2}}|"{{{{#if:|{{#ifeq:Template:Exists|Template:Exists|exists|exists}}|exists}}|{{#switch:p{{#switch:pexistence bq|p q=&s|p

q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}q|p

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}}{{#switch:{{#switch:pexistence bq|p q=&s|p

q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|{={|&p=||}=}|&e==|&nl=
|&*=*|&#=#|&:=:}}{{ {{#switch:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|{|&p|}|&e|&s|&nl|&*|&#|&:|*|**|***|#|##|###|:|::|:::|;=void|1x}}|{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}}}{{#switch:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|*=*|**=**|***=***|#=#|##=##|###=###|:=:|::=::|:::=:::|;=;}}{{ {{#switch:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|&s=1x|void}}| }}{{#ifeq:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|&|amp;}}}}" gives "Template:Exists" [http://sdnhq.undp.org/w/index.php?title=Special:ExpandTemplates&input=%22%7B%7Bexists%7c{{#switch:p{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}q|p

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q=%0d}}{{#switch:{{#switch:pexistence bq|p q=&s|p

q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|&p=%7c|&e=%3d|&s=+|&nl=%0d|&*=%2a|&#=%23|&:=%3a|%7B%7B%23switch%3Apexistence+bq%7Cp+q%3D%26s%7Cp%0Aq%3D%26nl%7Cp%2Aq%3D%26%2A%7Cp%23q%3D%26%23%7Cp%3Aq%3D%26%3A%7Cexistence+b%7D%7D}}%7D%7D%22]|"{{{{#if:|{{#ifeq:Template:Exists|Template:Exists|exists|exists}}|exists}}}}" gives "Template:Exists" {{#ifeq:gives||||||}} [8]}}|{{p{{#ifeq:existence b|1|2}}|existence b|"{{{{#if:|{{#ifeq:Template:Exists|Template:Exists|exists|exists}}|exists}}|{{#switch:p{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}q|p

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|&*=*|&#=#|&:=:}}{{ {{#switch:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|{|&p|}|&e|&s|&nl|&*|&#|&:|*|**|***|#|##|###|:|::|:::|;=void|1x}}|{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}}}{{#switch:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|*=*|**=**|***=***|#=#|##=##|###=###|:=:|::=::|:::=:::|;=;}}{{ {{#switch:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|&s=1x|void}}| }}{{#ifeq:{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|&|amp;}}}}" gives "Template:Exists" [http://sdnhq.undp.org/w/index.php?title=Special:ExpandTemplates&input=%22%7B%7Bexists%7c{{#switch:p{{#switch:pexistence bq|p q=&s|p q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}q|p

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q=%0d}}{{#switch:{{#switch:pexistence bq|p q=&s|p

q=&nl|p*q=&*|p#q=&#|p:q=&:|existence b}}|&p=%7c|&e=%3d|&s=+|&nl=%0d|&*=%2a|&#=%23|&:=%3a|%7B%7B%23switch%3Apexistence+bq%7Cp+q%3D%26s%7Cp%0Aq%3D%26nl%7Cp%2Aq%3D%26%2A%7Cp%23q%3D%26%23%7Cp%3Aq%3D%26%3A%7Cexistence+b%7D%7D}}%7D%7D%22]}}}}}}|{{p{{#ifeq:1|1|2}}|1|"{&#{{#if:|123;exists|123;exists}}|existence b|1}}" gives "Template:Exists" [9]}}}}}}|{{p{{#ifeq:0|1|2}}|0|{&#{{#if:|123;exists|123;exists}}|existence b|1|0}} gives Template:Exists [10]}}}}

• existence c
• Special:Allpages/existence
• Special:PrefixIndex/exist

{{Special:PrefixIndex/exist}} gives:

Another method is, of course, going to the web address concerned and seeing the content or a message that the page does not exist.

Branching applications

A typical application of existence detection is:

• producing the content of a page if it exists, otherwise some default

with the important special case:

• producing the content of a page if it exists, otherwise nothing

If the set of possible pages is limited then an alternative is creating them all, with the extra pages containing the default value(s), and unconditionally transcluding the pages.

CSS class

If existence is checked in order to hide red links, an alternative for {{#ifexist:foo|[[foo]]}} and {{exists|foo|[[foo]]}} is <span class="hidden-redlink">[[foo]]</span>, giving "foo", where we have the CSS specification

.hidden-redlink a.new { display: none; }

(which on Meta has been added to Mediawiki:Common.css).

Conversely an emphasized style could be used for red links, or only red links could be displayed.

Notes

See also

• w:Wikipedia:Village pump (technical)/Archive 9#Inconsistent limitations?
• w:Wikipedia:Village pump (technical)/Archive 9##ifexist limit
• w:Wikipedia:Village pump (technical)/Archive 33##ifexist limit
• w:Wikipedia:Template limits#Expensive parser function calls.
• w:Category:Pages with too many expensive parser function calls

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