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153 lines
7.1 KiB
Markdown
153 lines
7.1 KiB
Markdown
---
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date: 2014-11-25
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menu:
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main:
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parent: extras
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next: /extras/livereload
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prev: /extras/comments
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title: Cross-References
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toc: true
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weight: 40
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---
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Hugo makes it easy to link documents together with the `ref` and `relref` shortcodes. These shortcodes are also used to safely provide links to headings inside of your content, whether across documents or within a document. The only difference between `ref` and `relref` is whether the resulting URL is absolute (`http://1.com/about/`) or relative (`/about/`).
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## Using `ref` and `relref`
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```django
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{{</* ref "document" */>}}
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{{</* ref "#anchor" */>}}
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{{</* ref "document#anchor" */>}}
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{{</* relref "document" */>}}
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{{</* relref "#anchor" */>}}
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{{</* relref "document#anchor" */>}}
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```
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The single parameter to `ref` is a string with a content _document name_ (`about.md`), an in-document _anchor_ (`#who`), or both (`about.md#who`).
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### Document Names
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The _document name_ is the name of a document including the format extension; this may be just the filename, or the relative path from the `content/` directory. With a document `content/blog/post.md`, either format will produce the same result.
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{{</* relref "blog/post.md" */>}} ⇒ `/blog/post/`
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{{</* relref "post.md" */>}} ⇒ `/blog/post/`
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If you have multiple sections with the same filename, you should only use the relative path format, because the behaviour is _undefined_. So, if I also have a document `link/post.md`, the output of `ref` is unknown for `post.md`.
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{{</* relref "blog/post.md" */>}} ⇒ `/blog/post/`
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{{</* relref "post.md" */>}} ⇒ `/blog/post/` (maybe)
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{{</* relref "post.md" */>}} ⇒ `/link/post/` (maybe)
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{{</* relref "link/post.md" */>}} ⇒ `/link/post/`
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A relative document name must *not* begin with a slash (`/`).
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{{</* relref "/blog/post.md" */>}} ⇒ `""`
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### Anchors
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When an _anchor_ is provided by itself, the current page’s unique identifier will be appended; when an _anchor_ is provided with a document name, the found page's unique identifier will be appended.
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{{</* relref "#who" */>}} ⇒ `#who:9decaf7`
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{{</* relref "blog/post.md#who" */>}} ⇒ `/blog/post/#who:badcafe`
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More information about document unique identifiers and headings can be found [below]({{< ref "#hugo-heading-anchors" >}}).
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### Examples
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* `{{</* ref "blog/post.md" */>}}` ⇒ `http://1.com/blog/post/`
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* `{{</* ref "post.md#tldr" */>}}` ⇒ `http://1.com/blog/post/#tldr:caffebad`
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* `{{</* relref "post.md" */>}}` ⇒ `/blog/post/`
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* `{{</* relref "blog/post.md#tldr" */>}}` ⇒ `/blog/post/#tldr:caffebad`
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* `{{</* ref "#tldr" */>}}` ⇒ `#tldr:badcaffe`
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* `{{</* relref "#tldr" */>}}` ⇒ `#tldr:badcaffe`
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## Hugo Heading Anchors
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When using Markdown document types, Hugo generates heading anchors automatically. The generated anchor for this section is `hugo-heading-anchors`. Because the heading anchors are generated automatically, Hugo takes some effort to ensure that heading anchors are unique both inside a document and across the entire site.
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Ensuring heading uniqueness across the site is accomplished with a unique identifier for each document based on its path. Unless a document is renamed or moved between sections *in the filesystem*, the unique identifier for the document will not change: `blog/post.md` will always have a unique identifier of `81df004c333b392d34a49fd3a91ba720`.
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`ref` and `relref` were added so you can make these reference links without having to know the document’s unique identifier. (The links in document tables of contents are automatically up-to-date with this value.)
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{{</* relref "extras/crossreferences.md#hugo-heading-anchors" */>}}
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/extras/crossreferences/#hugo-heading-anchors:77cd9ea530577debf4ce0f28c8dca242
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> What follows is a deeper discussion of *why* and *how* Hugo generates heading anchors. It is not necessary to know this to use `ref` and `relref`, but it may be useful in understanding how some anchors may not match your expectations.
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### How to Generate a Heading Anchor
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Convert the text of the heading to lowercase.
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Hugo: A Fast & Modern Static Web Engine
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hugo: a fast & modern static web engine
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Replace anything that isn't an ASCII letter (`a-z`) or number (`0-9`) with a dash (`-`).
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hugo: a fast & modern static web engine
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hugo--a-fast---modern-static-web-engine
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Get rid of extra dashes.
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hugo--a-fast---modern-static-web-engine
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hugo-a-fast-modern-static-web-engine
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You have just converting the text of a heading to a suitable anchor. If your document has unique heading text, all of the anchors will be unique, too.
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#### Specifying Heading Anchors
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You can also tell Hugo to use a particular heading anchor.
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# Hugo: A Fast & Modern Static Web Engine {#hugo-main}
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Hugo will use `hugo-main` as the heading anchor.
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### What About Duplicate Heading Anchors?
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The technique outlined above works well enough, but some documents have headings with identical text, like the [shortcodes](/extras/shortcodes/) page—there are three headings with the text "Example". You can specify heading anchors manually:
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### Example {#example-1}
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### Example {#example-2}
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### Example {#example-3}
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It’s easy to forget to do that all the time, and Hugo is smart enough to do it for you. It just adds `-x` to the end of each heading it has already seen.
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* `### Example` ⇒ `example`
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* `### Example` ⇒ `example-1`
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* `### Example` ⇒ `example-2`
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Sometimes it's a little harder, but Hugo can recover from those, too, by adding more suffixes:
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* `# Heading` ⇒ `heading`
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* `# Heading 1` ⇒ `heading-1`
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* `# Heading` ⇒ `heading-1-1`
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* `# Heading` ⇒ `heading-1-2`
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* `# Heading 1` ⇒ `heading-2`
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This can even affect specified heading anchors that come after a generated heading anchor.
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* `# My Heading` ⇒ `my-heading`
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* `# My Heading {#my-heading}` ⇒ `my-heading-1`
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> This particular collision and override is unfortunate, but unavoidable because Hugo processes each heading for collision detection as it sees it during conversion.
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This technique works well for documents rendered on individual pages, like blog posts. What about on Hugo list pages?
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### Unique Heading Anchors in Lists
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Hugo converts each document from Markdown independently. it doesn’t know that `blog/post.md` has an "Example" heading that will collide with the "Example" heading in `blog/post2.md`. Even if it did know this, the addition of `blog/post3.md` should not cause the anchors for the headings in the other blog posts to change.
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Enter the document’s unique identifier. To prevent this sort of collision on
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list pages, Hugo always appends the document's to a generated heading anchor.
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So, the "Example" heading in `blog/post.md` actually turns into
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`#example:81df004…`, and the "Example" heading in `blog/post2.md` actually
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turns into `#example:8cf1599…`. All you have to know is the heading anchor that
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was generated, not the document identifier; `ref` and `relref` take care of the
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rest for you.
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<a href='{{</* relref "blog/post.md#example" */>}}'>Post Example</a>
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<a href='/blog/post.md#81df004…'>Post Example</a>
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[Post Two Example]({{</* relref "blog/post2.md#example" */>}})
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<a href='/blog/post2.md#8cf1599…'>Post Two Example</a>
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Now you know.
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