This Lua module is used in system messages, and on approximately 812,000 pages, or roughly 1% of all pages. Changes to it can cause immediate changes to the Wikipedia user interface. To avoid major disruption and server load, any changes should be tested in the module's /sandbox or /testcases subpages, or in your own module sandbox. The tested changes can be added to this page in a single edit. Please discuss changes on the talk page before implementing them.

This module can only be edited by administrators because it is transcluded onto one or more cascade-protected pages.

This module is rated as ready for general use. It has reached a mature state, is considered relatively stable and bug-free, and may be used wherever appropriate. It can be mentioned on help pages and other Wikipedia resources as an option for new users. To minimise server load and avoid disruptive output, improvements should be developed through sandbox testing rather than repeated trial-and-error editing.

This module directly imports all functions from the mw.ustring library. Documentation for each function can be found there.

The module takes an indefinite number of arguments. Arguments given as |s1=, |s2=, etc, are read first, and are used as strings. All remaining numerical arguments are coerced to number type if possible, and remain strings if not. If you wish for a numerical (i.e. unnamed or "|1=", "|2=") to remain a string, you can simply escape it by inserting \ at the beginning of the string.

Note that MediaWiki will always trim whitespace from named arguments; to give arguments with surrounding whitespace you must use unnamed parameters starting with \.

You can also wrap results in tags. All other unused arguments will be passed to frame:extensionTag

{{#invoke:Ustring|function_name|arg1|arg2|...}} is equivalent to mw.ustring.function_name( arg1, arg2, ... )

{{#invoke:Ustring|sub|s1=abcde|2|4}}

produces:

bcd

{{#invoke:Ustring|gsub|s1=1234|23|}}

produces:

14

&#{{#invoke:ustring|char|49|48|59}}

produces:




{{#invoke:Ustring|match|s1=abcde|s2=(c%w)}}

produces:

cd

Note: Only the first match is returned. Additional returns are omitted because mw.ustring.gsub's second return value is generally undesirable.

{{#invoke:Ustring|len|a string of twenty-nine chars}}

produces:

29

{{#invoke:Ustring|match
|s1={{Module:Ustring}}|%s%s%sif%snot%s[^%s]+%sthen.+%
<!--enter an actual newline character to match '\n'-->%s%s%send
|tag=syntaxhighlight|lang=lua}}

produces:

			if not fargs.tag then
				return (what(unpack(args)))		-- Outside parens truncate to first result avoiding tail call
			end
			local tagargs = {}
			for x, y in pairs(fargs) do
				if not fargsused[x] then tagargs[x] = y end
			end

Note that:

<syntaxhighlight lang="lua">{{#invoke:Ustring|match
|s1={{Module:Ustring}}|%s%s%sif%snot%s[^%s]+%sthen.+%
<!--enter an actual newline character to match '\n'-->%s%s%send}}</syntaxhighlight>

produces:

{{#invoke:Ustring|match
|s1={{Module:Ustring}}|%s%s%sif%snot%s[^%s]+%sthen.+%
<!--enter an actual newline character to match '\n'-->%s%s%send}}

Errors from accessing mw.ustring should be maintained, e.g.:

{{#invoke:Ustring|xyzzy}}

should produce:

Script error: The function "xyzzy" does not exist.

and

{{#invoke:Ustring|maxPatternLength}}

should produce:

Script error: "maxPatternLength" is not a function.