Help:Extension:ParserFunctions

The ParserFunctions extension provides ten additional parser functions to supplement those already present in MediaWiki. All the parser functions provided by this extension take the form:

{{ #functionname: argument 1 | argument 2 | argument 3 ... }}

#if:

{{#if: test string | value if true | value if false }}

This function tests whether the first parameter is 'non-empty'. It evaluates to false if the test string is empty or contains only whitespace characters (space, newline, etc).

{{#if: | true | false}} → false

{{#if: string | true | false}} → true

{{#if:      | true | false}} → false

{{#if:

| true | false}} → false

The test string is always interpreted as pure text, so mathematical expressions are not evaluated:

{{#if: 1==2 | true | false}} → true

Either or both the return values may be omitted:

{{#if: foo | true }} → true

{{#if: | true }} →

{{#if: foo | | false}} →

#ifeq:

This parser function compares two strings and determines whether they are identical.

{{#ifeq: string 1 | string 2 | value if true | value if false }}

If both strings are valid numerical values, the strings are compared numerically:

{{#ifeq: 01 | 1 | true | false}} → true

{{#ifeq: 0 | -0 | true | false}} → true

Otherwise the comparison is made as text; this comparison is case sensitive:

{{#ifeq: foo | bar | true | false}} → false

{{#ifeq: foo | Foo | true | false}} → false

{{#ifeq: "01" | "1" | true | false}} → false

Text inside <nowiki> tags is hashed within parser functions, resulting in errors:

{{#ifeq: <nowiki>foo</nowiki> | <nowiki>foo</nowiki> | true | false}} → false

#expr:

Type	Operators
Grouping (parentheses)	( )
Numbers	1234.5    2.4E5 e (2.718) pi (3.142)
Logic	or
	and
	= <> > < <= >=
Round	round
Binary	+ - mod
	* / div
	^
Unary	not ceil trunc floor abs ln sin cos tan acos asin atan
	e + -

This function evaluates a mathematical expression and returns the calculated value.

{{#expr: expression }}

The available operators are listed to the right, in order of precedence. See m:Help:Calculation for more details of the function of each operator. The accuracy and format of the result returned will vary depending on the operating system of the server running the wiki, and the number format of the site language.

When evaluating using boolean algebra, zero evaluates to false and any nonzero value, positive or negative, evaluates to true:

{{#expr: 1 and -1 }} → 1

An empty input expression returns an empty string. Invalid expressions return one of several error messages, which can be caught using the #iferror: function:

{{#expr: }} →

{{#expr: 1+ }} →

{{#expr: 1 foo 2 }} →

Some expressions may invoke floating-point errors when used with very large or very small numbers:

{{#expr: 20060618093259 mod 10000}} → 3259 in most cases, but may occasionally give -6357. This varies with the specification and configuration of the server running the wiki. See https://bugzilla.wikimedia.org/show_bug.cgi?id=6356.

#ifexpr:

This function evaluates a mathematical expression and returns one of two strings depending on the boolean value of the result:

{{#ifexpr: expression | value if true | value if false }}

The expression input is evaluated exactly as for #expr: above, with the same operators being available. The output is then evaluated as a boolean expression. This function is equivalent to one using #ifeq: and #expr: only:

{{#ifeq: {{#expr: expression }} | 1 | value if true | value if false }}

An empty input expression evaluates to false:

{{#ifexpr: | true | false}} → false

Either or both the return values may be omitted:

{{#ifexpr: 1 > 0 | true }} → true

{{#ifexpr: 1 < 0 | true }} →

{{#ifexpr: 1 > 0 | | false}} →

#switch:

This function compares one input value against several test cases, returning an associated string if a match is found.

{{#switch: comparison string
 | case = result
 | case = result
 | ...
 | case = result
 | default result
}}

The default result is returned if no case string matches the comparison string. In this syntax, the default result must be the last parameter and must not contain a raw equals sign. Alternatively, the default result may be explicitly declared with a case string of "#default"; default results declared in this way may be placed anywhere within the function:

{{#switch: test | foo = Foo | #default = Bar | baz = Baz }} → Bar

It is possible to have 'fall through' values, where several case strings return the same result string. This minimises duplication.

{{#switch: comparison string
 | case1 = result1
 | case2 
 | case3 
 | case4 = result2
 | case5 = result3
 | case6 
 | case7 = result4
 | default result
}}

Here cases 2, 3 and 4 all return result2; cases 6 and 7 both return result4

As with #ifeq:, the comparison is made numerically if both the comparison string and the case string being tested are numeric; or as case-sensitive string otherwise.

"Case" strings cannot contain raw equals signs:

{{#switch: 1=2 | 1=2 = raw | 1<nowiki>=<nowiki>2 = nowiki | 1&#61;2 = html | foo }} → html

#ifexist:

This function takes an input string, interprets it as a page title, and returns one of two values depending on whether or not the page exists on the local wiki.

{{#ifexist: page title | value if exists | value if doesn't exist }}

The function evaluates to true if the page exists, whether it contains content, is visibly blank (contains meta-data such as category links or magic words, but no visible content), is blank, or is a redirect. Only pages that are redlinked evaluate to false, including if the page used to exist but has been deleted.

{{#ifexist: Help:Extension:ParserFunctions | exists | doesn't exist }} → exists

{{#ifexist: XXXHelp:Extension:ParserFunctionsXXX | exists | doesn't exist }} → doesn't exist

The function evaluates to true for system messages that have been customised, and for special pages that are defined by the software.

{{#ifexist: Special:Watchlist | exists | doesn't exist }} → exists

{{#ifexist: Special:CheckUser | exists | doesn't exist }} → exists (because the CheckUser extension is installed on this wiki)

{{#ifexist: MediaWiki:Copyright | exists | doesn't exist }} → doesn't exist (because MediaWiki:Copyright has not been customised)

#ifexist: is considered an "expensive parser function", only a limited number of which can be included on any one page (including functions inside transcluded templates). When this limit is exceeded, the page is categorised into Category:Pages with too many expensive parser function calls, and any further #ifexist: functions automatically return false, whether the target page exists or not.

Tip for wiki admins: Configure the maximum number of allowed expensive parser functions using the $wgExpensiveParserFunctionLimit variable.

If a page checks a target using #ifexist:, then that page will appear in the Special:WhatLinksHere list for the target page. So if the code {{#ifexist:Foo}} were included live on this page (Help:Extension:ParserFunctions), Special:WhatLinksHere/Foo will list Help:Extension:ParserFunctions.

#iferror:

This function takes an input string and returns one of two results; the function evaluates to true if the input string contains an HTML object with class="error", as generated by other parser functions such as #expr:, #time: and #rel2abs:, template errors such as loops and recursions, and other 'failsoft' parser errors.

{{#iferror: test string | value if error | value if correct }}

One or both of the return strings can be omitted. If the correct string is omitted, the test string is returned if it is not erroneous. If the error string is also omitted, an empty string is returned on an error:

{{#iferror: {{#expr: 1 + 2 }} | error | correct }} → correct

{{#iferror: {{#expr: 1 + X }} | error | correct }} → error

{{#iferror: {{#expr: 1 + 2 }} | error }} → 3

{{#iferror: {{#expr: 1 + X }} | error }} → error

{{#iferror: {{#expr: 1 + 2 }} }} → 3

{{#iferror: {{#expr: 1 + X }} }} →

#time:

Code	Description	Current output
Year
Y	4-digit year.	2024
y	2-digit year.	24
L	1 or 0 whether it's a leap year or not	1
style="text-	ISO-	2024
rev:45208
Month
n	Month index, not zero-padded.	11
m	Month index, zero-padded.	11
M	An abbreviation of the month name, in the site language.	Nov
F	The full month name in the site language.	November
Week
W	ISO 8601 week number, zero-padded.	47
Day
j	Day of the month, not zero-padded.	21
d	Day of the month, zero-padded.	21
z	Day of the year (January 1 = 0)	325
D	An abbreviation for the day of the week. Rarely internationalised.	Thu
l	The full weekday name. Rarely internationalised.	Thursday
N	ISO 8601 day of the week.	4
w	number of the day of the week (Monday = 1).	4
Hour
a	"am" during the morning (00:00:00 → 11:59:59), "pm" otherwise (12:00:00 → 23:59:59)	pm
A	Uppercase version of a above.	PM
g	Hour in 12-hour format, not zero-padded.	9
h	Hour in 12-hour format, zero-padded.	09
G	Hour in 24-hour format, not zero-padded.	21
H	Hour in 24-hour format, zero-padded.	21
Minutes and seconds
i	Minutes past the hour, zero-padded.	01
s	Seconds past the minute, zero-padded.	35
U	Seconds since January 1 1970 00:00:00 GMT.	1732222895
Miscellaneous
L	1 if this year is a leap year in the Gregorian calendar, 0 otherwise	1
t	Number of days in the current month.	30
c	ISO 8601 formatted date, equivalent to Y-m-dTH:i:s+00:00.	2024-11-21T21:01:35+00:00
r	RFC 2822 formatted date, equivalent to D, j M Y H:i:s +0000, with weekday name and month name not internationalised.	Thu, 21 Nov 2024 21:01:35 +0000
Non-Gregorian calendars
Iranian
xij	Day of the month	1
xiF	Full month name	Azar
xin	Month index	9
xiY	Full year	1403
Hebrew
xjj	Day of the month	20
xjF	Full month name	Cheshvan
xjx	Genitive form of the month name	Cheshvan
xjn	Month number	2
xjY	Full year	5785
Thai solar
xkY	Full year	2567
Flags
xn	Format the next numeric code as a raw ASCII number.	In the Hindi language, {{#time:H, xnH}} produces ??, 06
xN	Like xn, but as a toggled flag, which endures until the end of the string or until the next appearance of xN in the string.
xr	Format the next number as a roman numeral. Only works for numbers up to 3000.	{{#time:xrY}} → MMXXIV
xg	Before a month flag (n, m, M, F), output the genitive form if the site language distinguishes between genitive and nominative forms.

This parser function takes a date and/or time construct and formats it according to the syntax given. A date/time object can be specified; the default is the value of the magic word {{CURRENTTIMESTAMP}} – that is, the time the page was last rendered into HTML.

{{#time: format string }}

{{#time: format string | date/time object }}

The list of accepted formatting codes is given in the table to the right. Any character in the formatting string that is not recognised is passed through unaltered. There are also two ways to escape characters within the formatting string:

1. A backslash followed by a formatting character is interpreted as a single literal character
2. characters enclosed in double quotes are considered literal characters, and the quotes are removed

In addition, the digraph xx is interpreted as a single literal "x".

{{#time: Y-m-d }} → 2024-11-21

{{#time: [[Y]] m d }} → 2024 11 21

{{#time: [[Y (year)]] }} → 2024 (24UTCpmThu, 21 Nov 2024 21:01:35 +0000)

{{#time: [[Y "(year)"]] }} → 2024 (year)

{{#time: i's" }} → 01'35"

The date/time object can be in any format accepted by PHP's strtotime() function. Both absolute (eg 20 December 2000) and relative (eg +20 hours) times are accepted.

The range of acceptable input is January 1 0100 → December 31 9999. Values outside this range will be misinterpreted:

{{#time: d F Y | 15 April 0099 }} → 15 April 0099

{{#time: d F Y | 15 April 10000 }} →

Full or partial absolute dates can be specified; the function will 'fill in' parts of the date that are not specified using the current values:

{{#time: Y | January 1 }} → 2024

A four-digit number is interpreted as hours and minutes if possible, and otherwise as year:

{{#time: Y m d H:i:s | 1959 }} → 1959 11 21 00:00:00 Input is treated as a time rather than a year.

{{#time: Y m d H:i:s | 1960 }} → 1960 11 21 00:00:00 Since 19:60 is no valid time, 1960 is treated as a year.

The fill-in feature is not consistent; some parts are filled in using the current values, others are not:

{{#time: Y m d H:i:s | January 1 }} → 2024 01 01 00:00:00

{{#time: Y m d H:i:s | February 2007 }} → 2007 02 01 00:00:00 Goes to the start of the month, not the current day.

The function performs a certain amount of date mathematics:

{{#time: d F Y | January 0 2008 }} → 2007 December 31 00:00:00

{{#time: d F | January 32 }} →

{{#time: d F | February 29 2008 }} → 29 February

{{#time: d F | February 29 2007 }} → 01 March

#rel2abs:

This function converts a relative file path into an absolute filepath.

{{#rel2abs: path }}

{{#rel2abs: path | base path }}

Within the path input, the following syntax is valid:

• . → the current level
• .. → "go up one level"
• /foo → "go down one level into the subdirectory /foo"

If the base path is not specified, the full page name of the page will be used instead:

{{#rel2abs: ./quok | Help:Foo/bar/baz }} → Help:Foo/bar/baz/quok

{{#rel2abs: ../quok | Help:Foo/bar/baz }} → Help:Foo/bar/quok

{{#rel2abs: ../. | Help:Foo/bar/baz }} → Help:Foo/bar

Invalid syntax, such as /. or /./, is ignored. Since no more than two consecutive full stops are permitted, sequences such as these can be used to separate successive statements:

{{#rel2abs: ../quok/. | Help:Foo/bar/baz }} → Help:Foo/bar/quok

{{#rel2abs: ../../quok | Help:Foo/bar/baz }} → Help:Foo/quok

{{#rel2abs: ../../../quok | Help:Foo/bar/baz }} → quok

{{#rel2abs: ../../../../quok | Help:Foo/bar/baz }} →

#titleparts:

This function separates a pagetitle into segments based on slashes, then returns some of those segments as output.

{{#titleparts: pagename | number of segments to return | first segment to return }}

If the first segment parameter is not specified, it defaults to "1". If the number of segments parameter is not speficied, it defaults to "0", which returns all the segments:

{{#titleparts: Talk:Foo/bar/baz/quok }} → Talk:Foo/bar/baz/quok

{{#titleparts: Talk:Foo/bar/baz/quok | 1 }} → Talk:Foo

{{#titleparts: Talk:Foo/bar/baz/quok | 2 }} → Talk:Foo/bar

{{#titleparts: Talk:Foo/bar/baz/quok | 2 | 2 }} → bar/baz

Negative values are accepted for number of segments, they translate to "add this value to the total number of segments", loosely equivalent to "count from the right":

{{#titleparts: Talk:Foo/bar/baz/quok | -1 }} → Talk:Foo/bar/baz

{{#titleparts: Talk:Foo/bar/baz/quok | -2 | 2 }} → bar

General points

Parser functions can be substituted by prefixing the hash character with subst::

{{subst:#ifexist: Help:Extension:ParserFunctions | [[Help:Extension:ParserFunctions]] | Help:Extension:ParserFunctions }} → the code [[Help:Extension:ParserFunctions]] will be inserted in the wikitext since the page Help:Extension:ParserFunctions exists.

The results of substituted parser functions are undefined if the expressions contain unsubstituted volatile code such as variables or other parser functions. For consistent results, all the volatile code in the expression to be evaluated must be substituted. See Help:Substitution.

Parser functions will mangle wikitable syntax, treating all the raw pipe characters as parameter divisors. To avoid this, most wikis create the template Template:! with its contents only a raw pipe character. This 'hides' the pipe from the MediaWiki parser, ensuring that it is not considered until after all the templates and variables on a page have been expanded. Alternatively, raw HTML table syntax can be used, although this is less intuitive and more error-prone.

Tip for wiki admins: You can improve the reliability of HTML table code (and other raw HTML input) by using HTML tidy. See Installing Tidy and $wgUseTidy.

Tip for wiki admins: You can also use the Pipe Escape extension to improve the handling of pipe characters.

Whitespace, including newlines, tabs, and spaces, is stripped from the beginning and end of all the parameters of these parser functions. If this is not desirable, adding any non-whitespace characters (including the HTML encoding for a whitespace character) will prevent further stripping:

{{#ifeq: foo            |            foo | equal | not equal }}

→ equal

{{#ifeq:  foo            |            foo  | equal | not equal }}

→ not equal

See also Help:Newlines and spaces.

HyperText Markup Language = structured text that uses logical links (hyperlinks) between nodes containing text.

PHP is the HyperText Preprocessor = the most popular programming language for the web