The following is only a primer on Go Templates. For an in-depth look into Go Templates, check the official [Go docs](https://golang.org/pkg/text/template/).
{{% /note %}}
Go Templates provide an extremely simple template language that adheres to the belief that only the most basic of logic belongs in the template or view layer.
## Basic Syntax
Go Templates are HTML files with the addition of [variables][variables] and [functions][functions]. Go Template variables and functions are accessible within `{{ }}`.
### Access a Predefined Variable
A _predefined variable_ could be a variable already existing in the
current scope (like the `.Title` example in the [Variables]({{<relref
"#variables" >}}) section below) or a custom variable (like the
`$address` example in that same section).
```go-html-template
{{ .Title }}
{{ $address }}
```
Parameters for functions are separated using spaces. The general syntax is:
```
{{ FUNCTION ARG1 ARG2 .. }}
```
The following example calls the `add` function with inputs of `1` and `2`:
```go-html-template
{{ add 1 2 }}
```
#### Methods and Fields are Accessed via dot Notation
Accessing the Page Parameter `bar` defined in a piece of content's [front matter][].
```go-html-template
{{ .Params.bar }}
```
#### Parentheses Can be Used to Group Items Together
```go-html-template
{{ if or (isset .Params "alt") (isset .Params "caption") }} Caption {{ end }}
```
## Variables {#variables}
Each Go Template gets a data object. In Hugo, each template is passed
a `Page`. In the below example, `.Title` is one of the elements
accessible in that [`Page` variable][pagevars].
With the `Page` being the default scope of a template, the `Title`
element in current scope (`.` -- "the **dot**") is accessible simply
by the dot-prefix (`.Title`):
```go-html-template
<title>{{ .Title }}</title>
```
Values can also be stored in custom variables and referenced later:
{{% note %}}
The custom variables need to be prefixed with `$`.
{{% /note %}}
```go-html-template
{{ $address := "123 Main St." }}
{{ $address }}
```
{{% warning %}}
For Hugo v0.47 and older versions, variables defined inside `if`
conditionals and similar are not visible on the outside.
See [https://github.com/golang/go/issues/10608](https://github.com/golang/go/issues/10608).
Hugo has created a workaround for this issue in [Scratch](/functions/scratch).
{{% /warning %}}
For **Hugo v0.48** and newer, variables can be re-defined using the
new `=` operator (new in Go 1.11).
Below example will work only in these newer Hugo versions. The example
prints "Var is Hugo Home" on the home page, and "Var is Hugo Page" on
all other pages:
```go-html-template
{{ $var := "Hugo Page" }}
{{ if .IsHome }}
{{ $var = "Hugo Home" }}
{{ end }}
Var is {{ $var }}
```
## Functions
Go Templates only ship with a few basic functions but also provide a mechanism for applications to extend the original set.
[Hugo template functions][functions] provide additional functionality specific to building websites. Functions are called by using their name followed by the required parameters separated by spaces. Template functions cannot be added without recompiling Hugo.
### Example 1: Adding Numbers
```go-html-template
{{ add 1 2 }}
<!-- prints 3 -->
```
### Example 2: Comparing Numbers
```go-html-template
{{ lt 1 2 }}
<!-- prints true (i.e., since 1 is less than 2) -->
```
Note that both examples make use of Go Template's [math functions][].
{{% note "Additional Boolean Operators" %}}
There are more boolean operators than those listed in the Hugo docs in the [Go Template documentation](https://golang.org/pkg/text/template/#hdr-Functions).
{{% /note %}}
## Includes
When including another template, you will need to pass it the data that it would
need to access.
{{% note %}}
To pass along the current context, please remember to include a trailing **dot**.
{{% /note %}}
The templates location will always be starting at the `layouts/` directory
within Hugo.
### Partial
The [`partial`][partials] function is used to include *partial* templates using
the syntax `{{ partial "<PATH>/<PARTIAL>.<EXTENSION>" . }}`.
Example of including a `layouts/partials/header.html` partial:
```go-html-template
{{ partial "header.html" . }}
```
### Template
The `template` function was used to include *partial* templates
in much older Hugo versions. Now it's useful only for calling
[*internal* templates][internal_templates]. The syntax is `{{ template
`if`, `else`, `with`, `or`, `and` and `not` provide the framework for handling conditional logic in Go Templates. Like `range`, `if` and `with` statements are closed with an `{{ end }}`.
One of the most powerful components of Go Templates is the ability to stack actions one after another. This is done by using pipes. Borrowed from Unix pipes, the concept is simple: each pipeline's output becomes the input of the following pipe.
Because of the very simple syntax of Go Templates, the pipe is essential to being able to chain together function calls. One limitation of the pipes is that they can only work with a single value and that value becomes the last parameter of the next pipeline.
A few simple examples should help convey how to use the pipe.
### Example 1: `shuffle`
The following two examples are functionally the same:
The following accesses the page parameter called "disqus_url" and escapes the HTML. This example also uses the [`index` function](/functions/index-function/), which is built into Go Templates:
{{ if or (or (isset .Params "title") (isset .Params "caption")) (isset .Params "attr") }}
Stuff Here
{{ end }}
```
Could be rewritten as
```go-html-template
{{ if isset .Params "caption" | or isset .Params "title" | or isset .Params "attr" }}
Stuff Here
{{ end }}
```
### Example 4: Internet Explorer Conditional Comments {#ie-conditional-comments}
By default, Go Templates remove HTML comments from output. This has the unfortunate side effect of removing Internet Explorer conditional comments. As a workaround, use something like this:
```go-html-template
{{ "<!--[if lt IE 9]>" | safeHTML }}
<scriptsrc="html5shiv.js"></script>
{{ "<![endif]-->" | safeHTML }}
```
Alternatively, you can use the backtick (`` ` ``) to quote the IE conditional comments, avoiding the tedious task of escaping every double quotes (`"`) inside, as demonstrated in the [examples](https://golang.org/pkg/text/template/#hdr-Examples) in the Go text/template documentation:
Notice how once we have entered the loop (i.e. `range`), the value of `{{ . }}` has changed. We have defined a variable outside of the loop (`{{$title}}`) that we've assigned a value so that we have access to the value from within the loop as well.
{{% /note %}}
### 2. Use `$.` to Access the Global Context
`$` has special significance in your templates. `$` is set to the starting value of `.` ("the dot") by default. This is a [documented feature of Go text/template][dotdoc]. This means you have access to the global context from anywhere. Here is an equivalent example of the preceding code block but now using `$` to grab `.Site.Title` from the global context:
{{<codefile="range-through-tags-w-global.html">}}
<ul>
{{ range .Params.tags }}
<li>
<ahref="/tags/{{ . | urlize }}">{{ . }}</a>
- {{ $.Site.Title }}
</li>
{{ end }}
</ul>
{{</code>}}
{{% warning "Don't Redefine the Dot" %}}
The built-in magic of `$` would cease to work if someone were to mischievously redefine the special character; e.g. `{{ $ := .Site }}`. *Don't do it.* You may, of course, recover from this mischief by using `{{ $ := . }}` in a global context to reset `$` to its default value.
{{% /warning %}}
## Whitespace
Go 1.6 includes the ability to trim the whitespace from either side of a Go tag by including a hyphen (`-`) and space immediately beside the corresponding `{{` or `}}` delimiter.
For instance, the following Go Template will include the newlines and horizontal tab in its HTML output:
```go-html-template
<div>
{{ .Title }}
</div>
```
Which will output:
```html
<div>
Hello, World!
</div>
```
Leveraging the `-` in the following example will remove the extra white space surrounding the `.Title` variable and remove the newline:
```go-html-template
<div>
{{- .Title -}}
</div>
```
Which then outputs:
```html
<div>Hello, World!</div>
```
Go considers the following characters _whitespace_:
*<kbd>space</kbd>
* horizontal <kbd>tab</kbd>
* carriage <kbd>return</kbd>
* newline
## Comments
In order to keep your templates organized and share information throughout your team, you may want to add comments to your templates. There are two ways to do that with Hugo.
### Go Templates comments
Go Templates support `{{/*` and `*/}}` to open and close a comment block. Nothing within that block will be rendered.
For example:
```go-html-template
Bonsoir, {{/* {{ add 0 + 2 }} */}}Eliott.
```
Will render `Bonsoir, Eliott.`, and not care about the syntax error (`add 0 + 2`) in the comment block.
### HTML comments
If you need to produce HTML comments from your templates, take a look at the [Internet Explorer conditional comments](#ie-conditional-comments) example. If you need variables to construct such HTML comments, just pipe `printf` to `safeHTML`. For example:
HTML comments are by default stripped, but their content is still evaluated. That means that although the HTML comment will never render any content to the final HTML pages, code contained within the comment may fail the build process.
{{% note %}}
Do **not** try to comment out Go Template code using HTML comments.
{{% /note %}}
```go-html-template
<!-- {{ $author := "Emma Goldman" }} was a great woman. -->
{{ $author }}
```
The templating engine will strip the content within the HTML comment, but will first evaluate any Go Template code if present within. So the above example will render `Emma Goldman`, as the `$author` variable got evaluated in the HTML comment. But the build would have failed if that code in the HTML comment had an error.
## Hugo Parameters
Hugo provides the option of passing values to your template layer through your [site configuration][config] (i.e. for site-wide values) or through the metadata of each specific piece of content (i.e. the [front matter][]). You can define any values of any type and use them however you want in your templates, as long as the values are supported by the [front matter format]({{< ref "front-matter.md#front-matter-formats" >}}).
## Use Content (`Page`) Parameters
You can provide variables to be used by templates in individual content's [front matter][].
An example of this is used in the Hugo docs. Most of the pages benefit from having the table of contents provided, but sometimes the table of contents doesn't make a lot of sense. We've defined a `notoc` variable in our front matter that will prevent a table of contents from rendering when specifically set to `true`.
Here is the example front matter (YAML):
```
---
title: Roadmap
lastmod: 2017-03-05
date: 2013-11-18
notoc: true
---
```
Here is an example of corresponding code that could be used inside a `toc.html` [partial template][partials]:
We want the *default* behavior to be for pages to include a TOC unless otherwise specified. This template checks to make sure that the `notoc:` field in this page's front matter is not `true`.
## Use Site Configuration Parameters
You can arbitrarily define as many site-level parameters as you want in your [site's configuration file][config]. These parameters are globally available in your templates.
For instance, you might declare the following:
{{<code-togglefile="config">}}
params:
copyrighthtml: "Copyright © 2017 John Doe. All Rights Reserved."
twitteruser: "spf13"
sidebarrecentlimit: 5
{{</code>}}
Within a footer layout, you might then declare a `<footer>` that is only rendered if the `copyrighthtml` parameter is provided. If it *is* provided, you will then need to declare the string is safe to use via the [`safeHTML` function][safehtml] so that the HTML entity is not escaped again. This would let you easily update just your top-level config file each January 1st, instead of hunting through your templates.
An alternative way of writing the "`if`" and then referencing the same value is to use [`with`][with] instead. `with` rebinds the context (`.`) within its scope and skips the block if the variable is absent:
Finally, you can pull "magic constants" out of your layouts as well. The following uses the [`first`][first] function, as well as the [`.RelPermalink`][relpermalink] page variable and the [`.Site.Pages`][sitevars] site variable.
```go-html-template
<nav>
<h1>Recent Posts</h1>
<ul>
{{- range first .Site.Params.SidebarRecentLimit .Site.Pages -}}
Go allows you to do more than what's shown here. Using Hugo's [`where` function][where] and Go built-ins, we can list only the items from `content/events/` whose date (set in a content file's [front matter][]) is in the future. The following is an example [partial template][partials]:
