Help:Linksearch

{{H:h|Reader toc}}

'''{{h:ml|Special:Linksearch}}''' is one of the {{h:ml|Help:Special page||special pages}}. It is an extension installed on Wikimedia wikis [http://svn.wikimedia.org/viewvc/mediawiki/trunk/extensions/LinkSearch].

Using the {{h:mlmw|externallinks table||externallinks table}} it provides a list of [[Help:link|link]]s in external link style from the site on which it is applied, to a given URL pattern. For each link the source page is provided, and the exact target, both linked. 

The URL pattern can be:
*a whole {{h:mlw|top-level domain||top-level domain}}, e.g. "*.nl": {{h:ml|Special:Linksearch/*.nl}}
*a {{h:mlw|second-level domain||second-level domain}}, e.g. "*.wikimedia.org": {{h:ml|Special:Linksearch/*.wikimedia.org}}; also a third-level domain etc.
*a full {{h:mlw|domain name||domain name}}, e.g. "www.wikimedia.org": {{h:ml|Special:Linksearch/www.wikimedia.org}}
*a full domain name and any first part of the rest of the URL, e.g.:
**"en.wikipedia.org/wiki/a": {{h:ml|Special:Linksearch/en.wikipedia.org/wiki/a}}
**"en.wikipedia.org/wiki/March_2007": {{h:ml|Special:Linksearch/en.wikipedia.org/wiki/March 2007}} (the underscore is required, even in the input box)
**"en.wikipedia.org/wiki/March_2007#2007_March_05": {{SERVER}}/w/index.php?title=Special:Linksearch&target=en.wikipedia.org/wiki/March_2007%232007_March_05 (the hash character is required in the input box, and %23 in the URL of the special page)

In the input box "http://" is allowed but not needed.

In the URL of the special page where the search string contains an anchor, or the first part of an anchor name, the hash character # has to be coded as "%23" and the required style is 
     w/index.php?title=Special:Linksearch&target=''URL''
In each of the styles
     wiki/Special:Linksearch/''target_page_name''#''anchor_name''
     wiki/Special:Linksearch/''target_page_name''%23''anchor_name''
the anchor is ignored. ("w" and "wiki" can be different on other than Wikimedia wikis.)

Remarks:
*Even if multiple URLs lead to the same target, with regard to capitalisation, multiple underscores, and using "index.php" or not, Linksearch is case-sensitive and also does not find alternatively written URLs. Therefore, when creating an external link, for optimal use of Linksearch, use a canonical form for the URL. In particular, if after following a link the address bar shows a modified URL, change the URL in the link to that.
*The list is {{ml|Help:Alphabetic_order||alphabetic}} in the URL. Note that an underscore, unlike a blank space, is alphabetically positioned between "Z" and "a".

For links in external link style, Linksearch provides backlinks of sections, which "Special:Whatlinkshere" does not for links in internal link style. For links in [[Help:Interwiki linking|interwiki link]] style there is no backlink feature at all.

On the other hand, links in internal link style provide existence detection. Also each of the three styles can have a different look, depending on CSS. 

Therefore it is useful to combine the advantages of various link styles adding "hidden  external links" to internal section links and to all interwiki links, except those for which the interlanguage link feature applies. This is done by adding <nowiki><span style="display:none">http://...</span></nowiki>; this can conveniently be done with a template, see below. Although no actual link is added (which would be superfluous because we have already an internal or interwiki link), it is recorded as external link, and therefore Linksearch can find it.

Since Linksearch allows specifying the first part of an anchor, it is useful, if anchor names are numerical or have a numerical end, to use leading zeros. Otherwise, when searching for links to e.g. "1", we also get links to "10", etc. This is e.g. applied in {{h:mlw|Portal:Current events/DateHeader2}}. More generally, if there are anchors "a" and "ab", it may or may not be desired that a search for links to "a" also   gives links to "ab"; if not, use an anchor "_a".

Also, if anchor names have multiple components, it is useful to put the most significant component first, e.g. if anchors indicate months or dates, we could have the format YYYY-MM, or YYYY-MM-DD, or in a year page MM-DD  (see also {{h:mlw|Calendar date|Big endian forms, starting with the year}}), with leading zeros (see also {{h:ml|Help:Date formatting and linking|Link to date content other than required for autoformatting}}). This applies also for page names, but since these are highly visible, as opposed to anchors, other considerations play a role too. In the case of sections, if for link targets another naming scheme is desired than for display of section headers, anchorscan be put explicitly instead of using section names. This is applied in {{h:mlw|Portal:Current events/DateHeader2}}, where the use in links of the names of explicitly put anchors is enforced by using pseudo sections, with displayed headers that cannot be used as anchors. 

In the case of multiple sections with the same name, the HTML produced has a HTML ID that is the section name, with, from the second occurrence, "_2", "_3", etc. appended. This does not apply when other anchors are used.

==Colon==
There seems to be a problem with a colon in the search pattern: it does not give any result, even though link targets with a colon are listed if the search pattern stops before the colon; if %3A is used as code for the colon, this code and the text after it are ignored. Compare [http://meta.wikimedia.org/w/index.php?title=Special%3ALinksearch&target=en.wikipedia.org%2Fwiki%2FPortal], [http://meta.wikimedia.org/w/index.php?title=Special%3ALinksearch&target=en.wikipedia.org%2Fwiki%2FPortal:], [http://meta.wikimedia.org/w/index.php?title=Special%3ALinksearch&target=en.wikipedia.org%2Fwiki%2FPortal%253A].

==See also==
*{{mlmw|Extension:LinkSearch}}
{{h:ml templates}}
*{{h:ml|Help:Section|Section linking}}.
{{h:f|langs=|enname=Linksearch}}