テンプレート処理の基本

テンプレートとは一つのファイルに表されるものであり、プロジェクト、テーマ、モジュールに対応したレイアウトディレクトリ内に置きます。 テンプレート内においては 変数、関数、メソッド を利用して、コンテント、リソース、データの内容を公開ページへと変換します。

たとえば以下の HTML テンプレートでは、まず $v1 と $v2 という変数を初期化して、HTML の段落内にそれを含めたコードを生成しています。

{{ $v1 := 6 }}
{{ $v2 := 7 }}
<p>The product of {{ $v1 }} and {{ $v2 }} is {{ mul $v1 $v2 }}.</p>

HTML テンプレートが最もよく利用されていますが、これ以外にも CSV、JSON、RSS、プレーンテキストなどのように、どのような 出力書式 に対してもテンプレートを生成することができます。

コンテキスト

テンプレートを作るにあたって理解しておくべき重要な考え方は コンテキスト (context) です。 これは各テンプレートに受け渡されるデータのことです。 このデータとは単純な値の場合もありますが、一般的には オブジェクト やそれに関連する メソッド のこともあります。

たとえば一つのページに対応するテンプレートは Page オブジェクトを受け取ります。 そしてその Page オブジェクトは、値を返したりアクションを実行したりするメソッドを提供します。

カレントコンテキスト

テンプレート内において、ドット (.) はカレントコンテキスト (current context) を表します。

<h2>{{ .Title }}</h2>

上の例におけるドットは Page オブジェクトを表しています。 そして Title メソッドを呼び出すことによって、フロントマター に定義されているタイトルを返すものです。

カレントコンテキストはテンプレート内において変わります。 たとえばテンプレートの上部において、コンテキストは Page オブジェクトとなるはずです。 しかし range や with のブロック内においてコンテキストへのバインドが再度行われるため、別の値や別のオブジェクトに変わります。

<h2>{{ .Title }}</h2>

{{ range slice "foo" "bar" }}
  <p>{{ . }}</p>
{{ end }}

{{ with "baz" }}
  <p>{{ . }}</p>
{{ end }}

In the example above, the context changes as we range through the slice of values. In the first iteration the context is “foo”, and in the second iteration the context is “bar”. Inside of the with block the context is “baz”. Hugo renders the above to:

<h2>My Page Title</h2>
<p>foo</p>
<p>bar</p>
<p>baz</p>

テンプレートコンテキスト

range ブロックや with ブロック内においてそのテンプレートに元々受け渡されていたコンテキストにアクセスする場合は、ドットの前にドル記号 ($) をつけます。

{{ with "foo" }}
  <p>{{ $.Title }} - {{ . }}</p>
{{ end }}

Hugo はこれを以下のようにレンダリングします。

<p>My Page Title - foo</p>

Actions

In the examples above the paired opening and closing braces represent the beginning and end of a template action, a data evaluation or control structure within a template.

A template action may contain literal values (boolean, string, integer, and float), variables, functions, and methods.

{{ $convertToLower := true }}
{{ if $convertToLower }}
  <h2>{{ strings.ToLower .Title }}</h2>
{{ end }}

In the example above:

• $convertToLower is a variable
• true is a literal boolean value
• strings.ToLower is a function that converts all characters to lowercase
• Title is a method on a the Page object

Hugo renders the above to:

    <h2>my page title</h2>

Whitespace

Notice the blank lines and indentation in the previous example? Although irrelevant in production when you typically minify the output, you can remove the adjacent whitespace by using template action delimiters with hyphens:

{{- $convertToLower := true -}}
{{- if $convertToLower -}}
  <h2>{{ strings.ToLower .Title }}</h2>
{{- end -}}

Hugo renders this to:

<h2>my page title</h2>

Whitespace includes spaces, horizontal tabs, carriage returns, and newlines.

Pipes

Within a template action you may pipe a value to function or method. The piped value becomes the final argument to the function or method. For example, these are equivalent:

{{ strings.ToLower "Hugo" }} → hugo
{{ "Hugo" | strings.ToLower }} → hugo

You can pipe the result of one function or method into another. For example, these are equivalent:

{{ strings.TrimSuffix "o" (strings.ToLower "Hugo") }} → hug
{{ "Hugo" | strings.ToLower | strings.TrimSuffix "o" }} → hug

These are also equivalent:

{{ mul 6 (add 2 5) }} → 42
{{ 5 | add 2 | mul 6 }} → 42

Line splitting

You can split a template action over two or more lines. For example, these are equivalent:

{{ $v := or .Site.Language.LanguageName .Site.Language.Lang }}

{{ $v := or
  .Site.Language.LanguageName
  .Site.Language.Lang
}}

You can also split raw string literals over two or more lines. For example, these are equivalent:

{{ $msg := "This is line one.\nThis is line two." }}

{{ $msg := `This is line one.
This is line two.`
}}

Variables

A variable is a user-defined identifier prepended with a dollar sign ($), representing a value of any data type, initialized or assigned within a template action. For example, $foo and $bar are variables.

Variables may contain scalars, slices, maps, or objects.

Use := to initialize a variable, and use = to assign a value to a variable that has been previously initialized. For example:

{{ $total := 3 }}
{{ range slice 7 11 21 }}
  {{ $total = add $total . }}
{{ end }}
{{ $total }} → 42

Variables initialized inside of an if, range, or with block are scoped to the block. Variables initialized outside of these blocks are scoped to the template.

With variables that represent a slice or map, use the index function to return the desired value.

{{ $slice := slice "foo" "bar" "baz" }}
{{ index $slice 2 }} → baz

{{ $map := dict "a" "foo" "b" "bar" "c" "baz" }}
{{ index $map "c" }} → baz

With variables that represent a map or object, chain identifiers to return the desired value or to access the desired method.

{{ $map := dict "a" "foo" "b" "bar" "c" "baz" }}
{{ $map.c }} → baz

{{ $homePage := .Site.Home }}
{{ $homePage.Title }} → My Homepage

Functions

Used within a template action, a function takes one or more arguments and returns a value. Unlike methods, functions are not associated with an object.

Go’s text/template and html/template packages provide a small set of functions, operators, and statements for general use. See the go-templates section of the function documentation for details.

Hugo provides hundreds of custom functions categorized by namespace. For example, the strings namespace includes these and other functions:

As shown above, frequently used functions have an alias. Use aliases in your templates to reduce code length.

When calling a function, separate the arguments from the function, and from each other, with a space. For example:

{{ $total := add 1 2 3 4 }}

Methods

Used within a template action and associated with an object, a method takes zero or more arguments and either returns a value or performs an action.

The most commonly accessed objects are the Page and Site objects. This is a small sampling of the methods available to each object.

Chain the method to its object with a dot (.) as shown below, remembering that the leading dot represents the current context.

{{ .Site.Title }} → My Site Title
{{ .Page.Title }} → My Page Title

The context passed into most templates is a Page object, so this is equivalent to the previous example:

{{ .Site.Title }} → My Site Title
{{ .Title }} → My Page Title

Some methods take an argument. Separate the argument from the method with a space. For example:

{{ $page := .Page.GetPage "/books/les-miserables" }}
{{ $page.Title }} → Les Misérables

Comments

Template comments are similar to template actions. Paired opening and closing braces represent the beginning and end of a comment. For example:

{{/* This is an inline comment. */}}
{{- /* This is an inline comment with adjacent whitespace removed. */ -}}

Code within a comment is not parsed, executed, or displayed. Comments may be inline, as shown above, or in block form:

{{/*
This is a block comment.
*/}}

{{- /*
This is a block comment with
adjacent whitespace removed.
*/ -}}

You may not nest one comment inside of another.

To render an HTML comment, pass a string through the safeHTML template function. For example:

{{ "<!-- I am an HTML comment. -->" | safeHTML }}
{{ printf "<!-- This is the %s site. -->" .Site.Title | safeHTML }}

Include

Use the template function to include one or more of Hugo’s embedded templates:

{{ template "_internal/google_analytics.html" . }}
{{ template "_internal/opengraph" . }}
{{ template "_internal/pagination.html" . }}
{{ template "_internal/schema.html" . }}
{{ template "_internal/twitter_cards.html" . }}

Use the partial or partialCached function to include one or more partial templates:

{{ partial "breadcrumbs.html" . }}
{{ partialCached "css.html" . }}

Create your partial templates in the layouts/partials directory.

Examples

This limited set of contrived examples demonstrates some of concepts described above. Please see the functions, methods, and templates documentation for specific examples.

Conditional blocks

See documentation for if, else, and end.

{{ $var := 42 }}
{{ if eq $var 6 }}
  {{ print "var is 6" }}
{{ else if eq $var 7 }}
  {{ print "var is 7" }}
{{ else if eq $var 42 }}
  {{ print "var is 42" }}
{{ else }}
  {{ print "var is something else" }}
{{ end }}

Logical operators

See documentation for and and or.

{{ $v1 := true }}
{{ $v2 := false }}
{{ $v3 := false }}
{{ $result := false }}

{{ if and $v1 $v2 $v3 }}
  {{ $result = true }}
{{ end }}
{{ $result }} → false

{{ if or $v1 $v2 $v3 }}
  {{ $result = true }}
{{ end }}
{{ $result }} → true

Loops

See documentation for range, else, and end.

{{ $s := slice "foo" "bar" "baz" }}
{{ range $s }}
  <p>{{ . }}</p>
{{ else }}
  <p>The collection is empty</p>
{{ end }}

Use the seq function to loop a specified number of times:

{{ $total := 0 }}
{{ range seq 4 }}
  {{ $total = add $total . }}
{{ end }}
{{ $total }} → 10

Rebind context

See documentation for with, else, and end.

{{ $var := "foo" }}
{{ with $var }}
  {{ . }} → foo
{{ else }}
  {{ print "var is falsy" }}
{{ end }}

To test multiple conditions:

{{ $v1 := 0 }}
{{ $v2 := 42 }}
{{ with $v1 }}
  {{ . }}
{{ else with $v2 }}
  {{ . }} → 42
{{ else }}
  {{ print "v1 and v2 are falsy" }}
{{ end }}

Access site parameters

See documentation for the Params method on a Site object.

With this site configuration:

baseURL: https://example.org
params:
  author:
    email: jsmith@example.org
    name: John Smith
  copyright-year: "2023"
  layouts:
    rfc_1123: Mon, 02 Jan 2006 15:04:05 MST
    rfc_3339: "2006-01-02T15:04:05-07:00"
  subtitle: The Best Widgets on Earth
title: ABC Widgets

baseURL = 'https://example.org'
title = 'ABC Widgets'
[params]
  copyright-year = '2023'
  subtitle = 'The Best Widgets on Earth'
  [params.author]
    email = 'jsmith@example.org'
    name = 'John Smith'
  [params.layouts]
    rfc_1123 = 'Mon, 02 Jan 2006 15:04:05 MST'
    rfc_3339 = '2006-01-02T15:04:05-07:00'

{
   "baseURL": "https://example.org",
   "params": {
      "author": {
         "email": "jsmith@example.org",
         "name": "John Smith"
      },
      "copyright-year": "2023",
      "layouts": {
         "rfc_1123": "Mon, 02 Jan 2006 15:04:05 MST",
         "rfc_3339": "2006-01-02T15:04:05-07:00"
      },
      "subtitle": "The Best Widgets on Earth"
   },
   "title": "ABC Widgets"
}

Access the custom site parameters by chaining the identifiers:

{{ .Site.Params.subtitle }} → The Best Widgets on Earth
{{ .Site.Params.author.name }} → John Smith

{{ $layout := .Site.Params.layouts.rfc_1123 }}
{{ .Site.Lastmod.Format $layout }} → Tue, 17 Oct 2023 13:21:02 PDT

Access page parameters

See documentation for the Params method on a Page object.

With this front matter:

date: 2023-10-17T15:11:37-07:00
params:
  author:
    email: jsmith@example.org
    name: John Smith
  display_related: true
title: Annual conference

date = 2023-10-17T15:11:37-07:00
title = 'Annual conference'
[params]
  display_related = true
  [params.author]
    email = 'jsmith@example.org'
    name = 'John Smith'

{
   "date": "2023-10-17T15:11:37-07:00",
   "params": {
      "author": {
         "email": "jsmith@example.org",
         "name": "John Smith"
      },
      "display_related": true
   },
   "title": "Annual conference"
}

Access the custom page parameters by chaining the identifiers:

{{ .Params.display_related }} → true
{{ .Params.author.name }} → John Smith