Utility Functions


html = a( url [, label=prettyUrl(url) ] )

Create a simple HTML <a> element.


n = ceil( n )

Alias for math.ceil().


path = chooseExistingFile( pathWithoutExtension, extensions )

Get the path of an existing file with any of the specified extensions. Returns nil if no file exists.


path = chooseExistingImage( pathWithoutExtension )

Get the path of an existing image file with any of the specified extensions. Returns nil if no image file exists.

Short form for chooseExistingFile(pathWithoutExtension, IMAGE_EXTENSIONS).


array = clampArray( array, length )

v1.3 Remove all items from array after the given length. Example:

# Latest Posts

{{ fori subpage in clampArray(subpages(), 3) }}
- {{ subpage.title }}
{{ end }}


css = cssPrefix( property, value )

Quick and dirty way of adding vendor-specific prefixes to a CSS property. Example:

local css = cssPrefix("flex", "auto")
-- css is "-ms-flex: auto; -moz-flex: auto; -webkit-flex: auto; flex: auto;"


string = date( format [, time=now ] )

Alias for (See the C docs for date format.)


html = entities( text )

Encode &, <, >, " and ' characters into HTML entities (&amp; etc.).


errorf( [ level=1, ] format, ... )

Raise an error with a formatted message.

Short form for error(F(format, ...), level).


string = F( format, ... )

Alias for string.format().


bool = fileExists( path )

Check if a file exists in the content folder.


bool = fileExistsInOutput( path [, skipRewriting=false ] )

Check if a file exists in the output folder, optionally without the usual rewriting of the path.


paths = files( folder [, onlyFilenames=false ] )
paths = files( folder, [ onlyFilenames=false, ] filenamePattern )
paths = files( folder, [ onlyFilenames=false, ] fileExtensionArray )
paths = files( folder, [ onlyFilenames=false, ] filterFunction )

Get a list of files in a folder inside the content folder. Examples:

local function dogFilter(filename)
	if filename:find"dog" then
		return true
	return false

local imagePaths   = files("/images", IMAGE_EXTENSIONS)
local psdFilenames = files("/resources/misc", true, "%.psd$")
local dogPaths     = files("/animal-files", dogFilter)


item, index = find( array, attribute, value )

Get the item in the array whose attribute is value. Returns nil if no item is found. Also see findAll()

local people = {
	{id=15, name="Harry"},
	{id=22, name="Jenny"},
print(find(people, "id", 22).name) -- Jenny


items = findAll( array, attribute, value )

Get all items in the array whose attribute is value. Also see find()


n = floor( n )

Alias for math.floor().


template = formatTemplate( format, valueTable )

Quick and dirty formatting of a template, presumably before using generateFromTemplate(). This replaces all instances of :key: with the corresponding field's value from valueTable. Example:

local templateUnformatted = [[
My dog, :dogName:, likes :thing:.
Other dogs probably like :thing: too!

local template = formatTemplate(templateUnformatted, {
	dogName = "Timmie the Dog",
	thing   = "bones",

generateFromTemplate("/dogs/", template)

Note that generateFromTemplate() can take page parameters as an argument that code blocks in the template can use. So, the above could be written more cleanly like this:

local template = [[
My dog, {{P.dogName}}, likes {{P.thing}}.
Other dogs probably like {{P.thing}} too!

generateFromTemplate("/dogs/", template, {
	dogName = "Timmie the Dog",
	thing   = "bones",


html = generatorMeta( [ hideVersion=false ] )

Get HTML generator meta tag (e.g. <meta name="generator" content="LuaWebGen 1.0.0">). This tag makes it possible to track how many websites use this generator, which is cool! This should be placed in the <head> element.


basename = getBasename( filename )

Get the filename without the extension. Example:

local basename = getBasename"blog/my-post.html"
print(basename) -- "my-post"


pathInCwd = getCompleteOutputPath( path )

Get the final (possibly rewritten) path for any file path. Example:

local path      = "/images/dog.png"
local pathInCwd = getCompleteOutputPath(path)
print(pathInCwd) -- "output/images/dog.png"

Note: The returned path is relative to current working directory, which is always the site root folder. The LuaWebGen API generally only handle paths relative to the content folder - the return value from getCompleteOutputPath() is an exception.


parsers = getDataBinaryParsers( )

v1.2 Get all parsers for binary data files (including those defined with config.dataBinaryParsers).


parsers = getDataTextParsers( )

v1.2 Get all parsers for text data files (including those defined with config.dataTextParsers). Example:

local defaultParsers = getDataTextParsers()

config.dataTextParsers = {
	wlua     = defaultParsers.lua,
	metainfo = defaultParsers.xml,


extension = getExtension( path )

Get the extension part of a path or filename.


filename = getFilename( path )

Get the filename part of a path.


pages = getGeneratedPages( )

v1.3 Get an array with all pages that has finished generating.


width, height = getImageDimensions( path )

Get the width and height of an image. Returns nil and a message on error.

This function may require Lua-GD.


keys = getKeys( table )

Get the keys from a table.


fileInfos = getOutputtedFiles( )

Get an array with information about outputted files/pages. Each item is a table with these fields:

  • path: Path to the written file in the output folder (after having been rewritten by config.rewriteOutputPath).
  • url: The relative URL for the file.
  • sourcePath: Path to the file in the content folder that triggered the creation of the written file (if there was one - otherwise this is an empty string).


for position, isMatch, capture1, capture2, ... in gmatchAndBetween( string, pattern )

v1.3 Match strings like string.gmatch() but also capture the strings between the matches. If isMatch is false then capture1 is the string between the last match and the next. (This string is never empty.) Example:

local text = "The year 2099 is going to be 1337"

-- Highlight numbers and make other text small.
for position, isMatch, numberOrStringBetween in gmatchAndBetween(text, "%d+") do
	if isMatch then
		local number = numberOrStringBetween
		local stringBetween = numberOrStringBetween


html = img( url [, alt="", title ] )
html = img( url [, alt="", useAltAsTitle=false ] )

Create a simple HTML <img> element.


index = indexOf( array, value )

Get the index of a value in an array. Returns nil if the value was not found.


for index, value in ipairsr( array )

Iterate backwards through an array.


bool = isAny( valueToCompare, value1, value2, ... )

Compare a value against a set of values.


bool = isValueHtml( value )

v1.3 Check if a value is a string, and that it looks like HTML code.

This function is used under the hood by echoSmart(), and by extension {{valueExpression}}.

isValueHtml("<a>foo</a>") -- true
isValueHtml("foo")        -- false
isValueHtml("<img> foo")  -- false


value = json.parse( jsonString [, filePathForErrorMessages ] )
value = json( jsonString [, filePathForErrorMessages ] )

v1.3 Parse a string containing JSON. Returns nil and a message on error. Note that the function may return false or nil on success, if that's what jsonString contains (but no message). Example:

local t = json.parse[[
	"foo": ["bar", false],
	"pi": 3.14
print([1]) -- bar

This is currently the only function available in the global json object.


n = max( n1, n2, ... )

Alias for math.max().


n = min( n1, n2, ... )

Alias for math.min().


stringBuilder = newStringBuilder( )

Create a handy string builder object, like so:

local b = newStringBuilder()

-- Add things.
b('<img src="icon.png">') -- One argument adds a plain value.
b(42) -- The one argument can be of any type.
b("<h1>%s</h1>", entities(page.title)) -- Multiple arguments act like string.format().

-- Get the contents.
local html = b() -- No arguments returns the concatenated string.


datetime = now( )

Get the current date and time as a datetime string.


for key, value in pairsSorted( table )

Like pairs(), iterate over the fields of a table, but in alphabetic order of the keys (sorted naturally). Note that the function does not detect additions or removals of table fields during the iteration.


encodedString = percent( string )

v1.4 Percent-encode all unreserved characters in a string for use in a URL (spaces become "%20", "/" become "%2F" etc.).

Also see url().


text = prettyUrl( url )

Make a URL look nice for displaying as text. Example:

local dogsUrl = ""
local label   = prettyUrl(dogsUrl) -- ""

echofRaw('<a href="%s">%s</a>', dogsUrl, label)

Also see a().


printf( format, ... )

Short form for print(F(format, ...)).


printfOnce( format, ... )

Print a formatted message only once. Meant for preventing too much spam in the console/log.


printObject( ... )

v1.1 Better printing of tables (though the function accepts any value).

Note: Does not print to the log file - only to stdout.


printOnce( ... )

Print value(s) only once. Meant for preventing too much spam in the console/log.


removeItem( array, value1, ... )

Remove one or more values from an array. Does not remove duplicate values.


number = round( number )

Round a number.


array = sortNatural( array [, attribute ] )

Naturally sort an array of strings. If the array contains tables you can sort by a specific attribute instead. Example:

local t = {"10","2","1"}
table.sort(t)  -- t is {"1","10","2"}
sortNatural(t) -- t is {"1","2","10"}

local objects = {
	{type="chair", type=1},
	{type="bed",   type=2},
	{type="house", type=3},
sortNatural(objects, "type")


parts = split( string, separatorPattern [, startIndex=1, plain=false ] )

Split a string by a pattern. Example:

local dogs = split("Fido,Grumpy,The Destroyer", ",")


html = summarize( html, maxCharacters [, keepSomeElements=false ] )

v1.3 Limit the amount of text and restrict allowed tags in an HTML string. The result can be used e.g. as the description for an item in an RSS feed.

If keepSomeElements is true then elements like <a>, <em>, <code>, <img> and <svg> are preserved. Elements like <br> and <bdo>, and any occurrences of the dir attribute, are always preserved.

Example for an RSS feed:

{{ fori subpage in clampArray(subpages(), 15) }}
	{{ if not subpage.isIndex }}
		<title>{{ subpage.title }}</title>
		<description><![CDATA[{{ summarize(subpage.content, 400, true) }}]]></description>
		<pubDate>{{"!%a, %d %b %Y %H:%M:%S GMT", toTime(subpage.publishDate)) }}</pubDate>
		<link>{{ url(subpage.permalink) }}</link>
		<guid>{{ url(subpage.permalink) }}</guid>
	{{ end }}
{{ end }}


html = thumb( imagePath, thumbWidth [, thumbHeight ] [, isLink=false ] )

Create a thumbnail from an image and get HTML code for showing the thumbnail. At least one of thumbWidth or thumbHeight must be a positive number. 0 means no restriction in that dimension. Note that sides may get cut off if the aspect ratio of the thumbnail is different from the image. Example:

{{ thumb("/images/gorillaz-fan-art.png", 400, 400, true) --[[ Size is 400x400.   ]] }}
{{ thumb("/images/a-big-tree.gif", 512, true)            --[[ Width is 512.      ]] }}
{{ thumb("/images/a-big-tree.gif", 512, 0, true)         --[[ Same as the above. ]] }}
{{ thumb("/images/1000-clown-cars.jpg", 0, 350, false)   --[[ Height is 350.     ]] }}

This function requires Lua-GD.


datetime = toDatetime( time )

Convert a time number to a datetime string.


luaString = toLua( value )

Convert a value to a Lua literal. Supported value types are: boolean, nil, number, string and table. Example:

-- Round-trip test for a string value.
local valueBefore = "foo"
local luaCode     = "return "..toLua(valueBefore)
local chunk       = loadstring(luaCode)
local valueAfter  = chunk()
assert(valueBefore == valueAfter)


table = toml.parse( tomlString [, filePathForErrorMessages ] )
table = toml( tomlString [, filePathForErrorMessages ] )

v1.3 Parse a string containing TOML. Returns nil and a message on error. Example:

local t = toml.parse[===[



print(t.people[2].name) -- Jenny

This is currently the only function available in the global toml object.


time = toTime( datetime )

Convert a datetime string to a normal time number value that standard libraries understand. Example:

local time        = toTime(page.publishDate)
local publishYear ="%Y", time)


string = trim( string )

Remove surrounding whitespace from a string.


string = trimNewlines( string )

Remove surrounding newlines from a string.


encodedUrl = url( urlString )

Percent-encode essential characters in a URL (spaces become %20 etc.). Does not encode %, so it's OK for the URL to already have some percent-encoded characters. If the URL is relative then the path part of site.baseUrl, if it has one, is prepended (keeping the URL relative). Examples:

print(url"/hello world.jpg")
-- Output if baseUrl is "":     /hello%20world.jpg
-- Output if baseUrl is "": /abc/hello%20world.jpg

Note: url() does not encode HTML entities, like ampersand, thus does not produce valid HTML:

local src  = url("/thumb.php?size=200&name=Hello world!")
local html = F('<img src="%s">', entities(src)) -- Correct.
local html = F('<img src="%s">', src) -- Incorrect.

Also see urlAbs(), urlRaw() and percent().


encodedUrl = urlAbs( urlString )

Same as url() but prepends the whole site.baseUrl to relative URLs, making them absolute.


bool = urlExists( url )

Check that a file for the URL exists. Useful e.g. as a sanity check after moving a bunch of pages (that now should have explicit aliases). Note that URLs to pages that have not been generated yet will make the function return false. See validateUrls() for multiple URL checks. Example:

function config.validate()
	local oldUrl = "/old-folder/my-post/"
	if not urlExists(oldUrl) then
		error("Page is missing: "..oldUrl)


urlPart = urlize( string )

Make a string look like a URL. Useful e.g. when converting page titles to URL slugs.

urlize("Hello, big world!") -- "hello-big-world"


encodedUrl = urlRaw( urlString )

v1.4 Same as url() but does not prepend anything to relative URLs.


validateUrls( urls )

Check that files for multiple URLs exist, and trigger an error if any don't exist. Useful e.g. as a sanity check after moving a bunch of pages (that now should have explicit aliases). See urlExists() for single URL checks. Example:

function config.validate()


warning( message )

Print a big warning message to the console. Nothing else happens.


warningOnce( message )

Print a big warning message to the console once only. Nothing else happens.

Context-Specific Functions

There are currently 3 contexts where code can run:


echo( value )

Output a string (or any other kind of value) from a template. HTML entities are encoded automatically in HTML and XML files. In other types of templates this function behaves exactly like echoRaw(). Available in templates.

Note: This function is used under the hood and it's often not necessary to call it manually. For example, these rows do the same thing:

{{ date"%Y" }}
{{ echo(date"%Y") }}


echof( format, ... )

Short form for echo(F(format, ...)).


echofRaw( format, ... )

Short form for echoRaw(F(format, ...)).


echoRaw( string )

Like echo(), output a string from a template, except HTML entities don't become encoded in this string. Available in templates.

echo   ("a < b") -- Output is "a &lt; b"
echoRaw("a < b") -- Output is "a < b"

Note: In templates, if an echo function isn't used then HTML entities are sometimes encoded and sometimes not - LuaWebGen tries to be smart about it:

{{ "<br>" }}            <!-- Output is "<br>"           -->
{{ "Foo <br>" }}        <!-- Output is "Foo &lt;br&gt;" -->

{{ echo"<br>" }}        <!-- Output is "&lt;br&gt;"     -->
{{ echo"Foo <br>" }}    <!-- Output is "Foo &lt;br&gt;" -->

{{ echoRaw"<br>" }}     <!-- Output is "<br>"           -->
{{ echoRaw"Foo <br>" }} <!-- Output is "Foo <br>"       -->


echoSmart( value )

v1.3 Output a value from a template in a "smart" way. This function calls echoRaw() if value looks like HTML. Otherwise it calls echo(), unless the value is nil is which case it does nothing.

This function is used under the hood by {{valueExpression}}.


page = generateFromTemplate( path, templateString )
page = generateFromTemplate( path, templateString, pageParameters )
page = generateFromTemplate( path, templateString, pageInitializer )

Generate a page from a template string. Available in config.before() and config.after().

path is the file path the template would have had if it was loaded from a file in the content folder, e.g. "/blog/2020/06/". It is used to determine the template file type and URL for the page.

The function optionally takes page parameters as an argument for code blocks in the template, or it's layout, to use.


local path     = "/dogs/"
local template = "# Fido\n\nFido is fluffy!"
local page     = generateFromTemplate(path, template)
printf("We generated page '%s'.", page.url)
local template = [[
page.title  = "Carpets"
page.layout = "normalPageWithFooter"

Experience the best carpets around!

local params = {
	creditsInPageFooter = {
		{what="Fabric", who="Soft Inc."},
		{what="Paint",  who="Bob Bobson Co."},

generateFromTemplate("/products/", template, params)

v1.1 If the pageInitializer argument is given, it should be a callback function. It will execute before any embedded code in the template just as if the function's body was the topmost part of the header code block. The function also will be called in the template context, so the usual global objects, like page or params, are accessible like normally in a template. In other words, this is a good place to update page properties.

This example has the same outcome as the previous example:

local template = [[
Experience the best carpets around!

generateFromTemplate("/products/", template, function()
	page.title  = "Carpets"
	page.layout = "normalPageWithFooter"

	P.creditsInPageFooter = {
		{what="Fabric", who="Soft Inc."},
		{what="Paint",  who="Bob Bobson Co."},


html = include( filename )
html = include( filename, extraArgument1, ... ) v1.4

Get the result of a HTML template from the layouts folder. Available in templates.

Note: Exclude the extension from the filename (e.g. include("footer")).

Extra arguments can be sent to the layout. They can be grabbed using the vararg expression (...) in file scope. Example:

<!-- content/laugh.html -->
{{ include("repeat", "ha", 3) }}

<!-- layouts/repeat.html -->
<p> I say
local stringToRepeat, numberOfRepeats = ...


bool = isCurrentUrl( url )

Check if the relative URL of the current page is url. Available in templates. Example:

{{ if isCurrentUrl"/blog/last-post/" }}
You've reached the end!
{{ end }}


bool = isCurrentUrlBelow( urlPrefix )

Check if the relative URL of the current page starts with urlPrefix. Available in templates. Example:

{{ local class = isCurrentUrlBelow"/blog/" and "current" or "" }}

<a href="/blog/" class="{{ class }}">Blog</a>


lock( )

Prevent further changes to page properties, such as page.isDraft and page.publishDate. This allows the current page to be referenced elsewhere (e.g. in index pages) even during it's generation, preventing circular dependencies. Also see config.autoLockPages.

Here's an example of two pages referencing each other through subpages():

page.title = "Cute Kittens"
-- page.title = "Sly Turtles" -- Error!

(imagine cute kittens)

Also see:
{{ for subpage in subpages() }}
- [{{ subpage.title }}]({{ url(subpage.url) }})
{{ end }}

page.title = "Playful Puppies"

(imagine playful puppies)

Also see:
{{ for subpage in subpages() }}
- [{{ subpage.title }}]({{ url(subpage.url) }})
{{ end }}


outputRaw( path, contents )

Output any data to a file in the output folder. Available in config.before() and config.after(). Example:

outputRaw("/docs/versions.txt", "Version 1\nReleased: 2002-10-16\n")

Also see preserveRaw()


preserveRaw( path )

Prevent a previously outputted raw file from being cleaned out from the output folder after the site generation is done. This function makes it possible to not having to call outputRaw() every time the site builds which could decrease build time. Available in config.before() and config.after().

Note: This functionality is automatically used for all non-template files (like images or JavaScript files) in the content folder.


pages = subpages( [ includeCurrentPage=false ] ) -- Available in templates.
pages = subpages( pathPrefix ) v1.3 -- Available anywhere.

Recursively get all (non-special) pages in the current folder and below (or pages matching pathPrefix), sorted by page.publishDate from newest to oldest. Intended for index pages, but can be used anywhere. Example:

# Blog Archive

{{ fori subpage in subpages() }}
- [{{"%Y-%m-%d", toTime(subpage.publishDate)) }} {{ subpage.title }}]({{ url(subpage.url) }})
{{ end }}

Note: Two pages in the same folder cannot normally request all subpages - that would result in an infinite loop as LuaWebGen tries to generate all subpages before returning a list of them. However, you can solve this by calling lock() in all relevant pages, or enable config.autoLockPages. This will prevent further changes to essential page information (such as page.isDraft or page.publishDate) and thus allowing the page to be referenced elsewhere even during it's generation.

Another possible solution is to generate at least one of those two pages in config.after().

Page updated: 2021-07-09