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+---
+aliases:
+- /layout/functions/
+date: 2013-07-01
+linktitle: Functions
+menu:
+  main:
+    parent: layout
+next: /templates/variables
+prev: /templates/go-templates
+title: Hugo Template Functions
+weight: 20
+---
+
+Hugo uses the excellent Go html/template library for its template engine.
+It is an extremely lightweight engine that provides a very small amount of
+logic. In our experience it is just the right amount of logic to be able
+to create a good static website.
+
+Go templates are lightweight but extensible. Hugo has added the following
+functions to the basic template logic.
+
+(Go itself supplies built-in functions, including comparison operators
+and other basic tools; these are listed in the
+[Go template documentation](http://golang.org/pkg/text/template/#hdr-Functions).)
+
+## General
+
+### isset
+Return true if the parameter is set.
+Takes either a slice, array or channel and an index or a map and a key as input.
+
+e.g. {{ if isset .Params "project_url" }} {{ index .Params "project_url" }}{{ end }}
+
+### echoParam
+If parameter is set, then echo it.
+
+e.g. {{echoParam .Params "project_url" }}
+
+### eq
+Return true if the parameters are equal.
+
+e.g.
+    {{ if eq .Section "blog" }}current{{ end}}"
+
+### first
+Slices an array to only the first X elements.
+
+Works on [lists](/templates/list/), [taxonomies](/taxonomies/displaying/), [terms](/templates/terms/), [groups](/templates/list/)
+
+e.g.
+    {{ range first 10 .Data.Pages }}
+        {{ .Render "summary"}}
+    {{ end }}
+
+### where
+Filters an array to only elements containing a matching value for a given field.
+
+Works on [lists](/templates/list/), [taxonomies](/taxonomies/displaying/), [terms](/templates/terms/), [groups](/templates/list/)
+
+e.g.
+
+    {{ range where .Data.Pages "Section" "post" }}
+       {{ .Content}}
+    {{ end }}
+
+*where and first can be stacked*
+
+e.g.
+
+    {{ range first 5 (where .Data.Pages "Section" "post") }}
+       {{ .Content}}
+    {{ end }}
+
+### in
+Checks if an element is in an array (or slice) and returns a boolean.  The elements supported are strings, integers and floats (only float64 will match as expected).  In addition, it can also check if a substring exists in a string.
+
+e.g.
+    {{ if in .Params.tags "Git" }}Follow me on GitHub!{{ end }}
+or
+    {{ if in "this string contains a substring" "substring" }}Substring found!{{ end }}
+
+### intersect
+Given two arrays (or slices), this function will return the common elements in the arrays.  The elements supported are strings, integers and floats (only float64).
+
+A useful example of this functionality is a 'similar posts' block.  Create a list of links to posts where any of the tags in the current post match any tags in other posts.
+
+e.g.
+    <ul>
+    {{ $page_link := .Permalink }}
+    {{ $tags := .Params.tags }}
+    {{ range .Site.Recent }}
+        {{ $page := . }}
+        {{ $has_common_tags := intersect $tags .Params.tags | len | lt 0 }}
+        {{ if and $has_common_tags (ne $page_link $page.Permalink) }}
+            <li><a href="{{ $page.Permalink }}">{{ $page.Title }}</a></li>
+        {{ end }}
+    {{ end }}
+    </ul>
+
+
+## Math
+
+### add
+Adds two integers.
+
+e.g. {{add 1 2}} → 3
+
+### sub
+Subtracts two integers.
+
+e.g. {{sub 3 2}} → 1
+
+### div
+Divides two integers.
+
+e.g. {{div 6 3}} → 2
+
+### mul
+Multiplies two integers.
+
+e.g. {{mul 2 3}} → 6
+
+### mod
+Modulus of two integers.
+
+e.g. {{mod 15 3}} → 0
+
+### modBool
+Boolean of modulus of two integers.
+true if modulus is 0.
+
+e.g. {{modBool 15 3}} → true
+
+## Strings
+
+### urlize
+Takes a string and sanitizes it for usage in URLs, converts spaces to "-".
+
+e.g. &lt;a href="/tags/{{ . | urlize }}"&gt;{{ . }}&lt;/a&gt;
+
+### safeHtml
+Declares the provided string as "safe" so Go templates will not filter it.
+
+e.g. {{ .Params.CopyrightHTML | safeHtml }}
+
+### lower
+Convert all characters in string to lowercase.
+
+e.g. {{lower "BatMan"}} → "batman"
+
+### upper
+Convert all characters in string to uppercase.
+
+e.g. {{upper "BatMan"}} → "BATMAN"
+
+### title
+Convert all characters in string to titlecase.
+
+e.g. {{title "BatMan"}} → "Batman"
+
+### highlight
+Take a string of code and a language, uses Pygments to return the syntax
+highlighted code in HTML. Used in the [highlight shortcode](/extras/highlighting).