Jekyll With Liquid

博客原文：http://huangyanxiang.com/2017/09/20/jekyll-with-liquid.html

Jekyll的模板中可使用Liquid語法進行取值，計算和數據處理，若是僅僅只爲了使用Jekyll撰寫博客文章，你能夠不須要了解liquid, 可是若是你須要定製Jekyll的主題，靈活的控制你的站點，你確實有必要了解一些liquid相關的語法。

Liquid和大多數模板語言相似，也是比較簡單的。

官方網址：

• GitHub Project
• GitHub Pages Doc
• 官網

概覽

Liquid能夠分爲objects, tags, and filters.

使用英文雙大括號對objects進行取值。

獲取頁面的標題:

{{ page.title }}

標籤，例如：條件控制，循環，都是包裹在{% 和 %}中的。

若是user不爲空，則輸出user.name:

{% if user %}
  Hello {{ user.name }}!
{% endif %}

對於filter, 你能夠理解爲提供了一系列經常使用的方法，而且支持管道操做。

對url地址添加.html後綴：

{{ "/my/fancy/url" | append: ".html" }}

輸出：

/my/fancy/url.html

首字母大寫，而後在前面添加Hello :

{{ "adam!" | capitalize | prepend: "Hello " }}

輸出：

Hello Adam!

是否是很easy?

操做符

Liquid包含以下操做符：

==	equals
!=	does not equal
>	greater than
<	less than
>=	greater than or equal to
<=	less than or equal to
or	logical or
and	logical and

舉個栗子，你一看就懂得。

{% if product.title == "Awesome Shoes" %}
  These shoes are awesome!
{% endif %}

{% if product.type == "Shirt" or product.type == "Shoes" %}
  This is a shirt or a pair of shoes.
{% endif %}

另外還有一個操做符：contains, 它能夠判斷字符串的包含，還能夠判斷數組中的字符串包含關係（若是數組中是非字符串的，是不能判斷出來的）。

{% if product.title contains 'Pack' %}
  This product's title contains the word Pack.
{% endif %}

{% if product.tags contains 'Hello' %}
  This product has been tagged with 'Hello'.
{% endif %}

數據類型

和大多數語言同樣，Liquid也有經常使用的數據類型。

Boolean

true or false

{% assign foo = true %}
{% assign bar = false %}

Number

統一都叫數字，不分整型，浮點型了

{% assign my_int = 25 %}
{% assign my_float = 39.756 %}

String

使用單引號或雙引號包裹的字符串。

{% assign my_string = "Hello World!" %}

Nil

相似js的undefined.

Array

Liquid中沒法單獨定義出數組，不過你可使用filter處理獲得數組。

數組的取值採用廣泛接受的索引取值方式：

{{ site.users[0] }}
{{ site.users[1] }}
{{ site.users[3] }}

對於數組比較經常使用的還有遍歷操做：

{% for user in site.users %}
  {{ user }}
{% endfor %}

Truthy and Falsy

這兩個不叫數據類型，可是是條件判斷的依據，他們叫：真 和 假。何時是真？何時是假？很簡單，你只須要記着：Nil 和 false 是假，其餘的都是真就對了，包括0，空字符串都是真。

	truthy	falsy
true	•
false		•
nil		•
string	•
empty string	•
0	•
integer	•
float	•
array	•
empty array	•
page	•
EmptyDrop	•

Tags

Tags你能夠理解爲Liquid的關鍵詞，如條件判斷if, 循環語句for, Tag是 {% 和 %} 包裹起來的。

註釋

註釋是不會被Liquid引擎處理的。Liquid的註釋既能夠做用於單行，又能夠做用於多行。

{% comment %} line comment {% endcomment %}
{% comment %}
block comment
{% endcomment %}

條件流程控制

直接看例子吧。

{% if product.title == 'Awesome Shoes' %}
  These shoes are awesome!
{% endif %}

{% unless product.title == 'Awesome Shoes' %}
  These shoes are not awesome.
{% endunless %}

equals

{% if product.title != 'Awesome Shoes' %}
  These shoes are not awesome.
{% endif %}

{% if customer.name == 'kevin' %}
  Hey Kevin!
{% elsif customer.name == 'anonymous' %}
  Hey Anonymous!
{% else %}
  Hi Stranger!
{% endif %}

{% assign handle = 'cake' %}
{% case handle %}
  {% when 'cake' %}
     This is a cake
  {% when 'cookie' %}
     This is a cookie
  {% else %}
     This is not a cake nor a cookie
{% endcase %}

循環遍歷

{% for i in (1..5) %}
  {% if i == 4 %}
    {% break %}
  {% else %}
    {{ i }}
  {% endif %}
{% endfor %}

{% for i in (1..5) %}
  {% if i == 4 %}
    {% continue %}
  {% else %}
    {{ i }}
  {% endif %}
{% endfor %}

limit

<!-- if array = [1,2,3,4,5,6] -->
{% for item in array limit:2 %}
  {{ item }}
{% endfor %}

1 2

offset

<!-- if array = [1,2,3,4,5,6] -->
{% for item in array offset:2 %}
  {{ item }}
{% endfor %}

3 4 5 6

range

{% for i in (3..5) %}
  {{ i }}
{% endfor %}

{% assign num = 4 %}
{% for i in (1..num) %}
  {{ i }}
{% endfor %}

3 4 5
1 2 3 4

reversed

<!-- if array = [1,2,3,4,5,6] -->
{% for item in array reversed %}
  {{ item }}
{% endfor %}

6 5 4 3 2 1

cycle, 週期循環的意思。

{% cycle 'one', 'two', 'three' %}
{% cycle 'one', 'two', 'three' %}
{% cycle 'one', 'two', 'three' %}
{% cycle 'one', 'two', 'three' %}

one
two
three
one

tablerow, 快速構建表格的行。

<table>
{% tablerow product in collection.products %}
  {{ product.title }}
{% endtablerow %}
</table>

<table>
  <tr class="row1">
    <td class="col1">
      Cool Shirt
    </td>
    <td class="col2">
      Alien Poster
    </td>
    <td class="col3">
      Batman Poster
    </td>
    <td class="col4">
      Bullseye Shirt
    </td>
    <td class="col5">
      Another Classic Vinyl
    </td>
    <td class="col6">
      Awesome Jeans
    </td>
  </tr>
</table>

{% tablerow product in collection.products cols:2 %}
  {{ product.title }}
{% endtablerow %}

<table>
  <tr class="row1">
    <td class="col1">
      Cool Shirt
    </td>
    <td class="col2">
      Alien Poster
    </td>
  </tr>
  <tr class="row2">
    <td class="col1">
      Batman Poster
    </td>
    <td class="col2">
      Bullseye Shirt
    </td>
  </tr>
  <tr class="row3">
    <td class="col1">
      Another Classic Vinyl
    </td>
    <td class="col2">
      Awesome Jeans
    </td>
  </tr>
</table>

{% tablerow product in collection.products cols:2 limit:3 %}
  {{ product.title }}
{% endtablerow %}

{% tablerow product in collection.products cols:2 offset:3 %}
  {{ product.title }}
{% endtablerow %}

<!--variable number example-->

{% assign num = 4 %}
<table>
{% tablerow i in (1..num) %}
  {{ i }}
{% endtablerow %}
</table>

<!--literal number example-->

<table>
{% tablerow i in (3..5) %}
  {{ i }}
{% endtablerow %}
</table>

變量

Liquid, 支持變量的定義和計算。

assign

{% assign my_variable = false %}
{% if my_variable != true %}
  This statement is valid.
{% endif %}

{% assign foo = "bar" %}
{{ foo }}

capture

{% capture my_variable %}I am being captured.{% endcapture %}
{{ my_variable }}

I am being captured.

{% assign favorite_food = 'pizza' %}
{% assign age = 35 %}

{% capture about_me %}
I am {{ age }} and my favorite food is {{ favorite_food }}.
{% endcapture %}

{{ about_me }}

I am 35 and my favourite food is pizza.

Creates a new number variable, and increases its value by one every time it is called. 
The initial value is 0.

{% increment my_counter %}
{% increment my_counter %}
{% increment my_counter %}

0
1
2

Variables created through the increment tag are independent from variables created through assign or capture.

{% assign var = 10 %}
{% increment var %}
{% increment var %}
{% increment var %}
{{ var }}

0
1
2
10

{% decrement variable %}
{% decrement variable %}
{% decrement variable %}

-1
-2
-3

Filters

Liquid提供了一些經常使用的過濾器（方法）。

abs

{{ -17 | abs }}
17

{{ "-19.86" | abs }}
19.86

append, prepend

{% assign filename = "/index.html" %}
{{ "website.com" | append: filename }}
website.com/index.html

capitalize

首字母大寫。

{{ "title" | capitalize }}
Title
{{ "my great title" | capitalize }}
My great title

date

{{ article.published_at | date: "%a, %b %d, %y" }}
Fri, Jul 17, 15
{{ article.published_at | date: "%Y" }}
2015
{{ "March 14, 2016" | date: "%b %d, %y" }}
Mar 14, 16

To get the current time, pass the special word "now" (or "today") to date:
This page was last updated at {{ "now" | date: "%Y-%m-%d %H:%M" }}.
This page was last updated at 2017-06-29 14:45.

default

{{ product_price | default: 2.99 }}
2.99
{% assign product_price = 4.99 %}
{{ product_price | default: 2.99 }}
4.99
{% assign product_price = "" %}
{{ product_price | default: 2.99 }}
2.99

lstrip, rstrip, strip

去除句子首部的空白字符。

{{ "          So much room for activities!          " | lstrip }}
So much room for activities!

去除句子尾部的空白字符。

{{ "          So much room for activities!          " | rstrip }}
          So much room for activities!

去除首尾的空白字符。

{{ "          So much room for activities!          " | strip }}
So much room for activities!

plus, minus, times, divided_by

加，減，乘，除運算。

{{ 16 | divided_by: 4 }}
4
{{ 5 | divided_by: 3 }}
1
{{ 20 | divided_by: 7.0 }}
2.857142857142857
{% assign my_integer = 7 %}
{% assign my_float = my_integer | times: 1.0 %}
{{ 20 | divided_by: my_float }}
2.857142857142857

remove, remove_first

{{ "I strained to see the train through the rain" | remove: "rain" }}
I sted to see the t through the 
{{ "I strained to see the train through the rain" | remove_first: "rain" }}
I sted to see the train through the rain

replace, replace_first

{{ "Take my protein pills and put my helmet on" | replace: "my", "your" }}
Take your protein pills and put your helmet on
{% assign my_string = "Take my protein pills and put my helmet on" %}
{{ my_string | replace_first: "my", "your" }}
Take your protein pills and put my helmet on

slice

Returns a substring of 1 character beginning at the index specified by the argument passed in. An optional second argument specifies the length of the substring to be returned.

截取指定長度的字符串，第二個表示長度，第一個表示索引，從0開始，若是爲負數，從後面往前數，從-1開始。

{{ "Liquid" | slice: 0 }}
L
{{ "Liquid" | slice: 2 }}
q
{{ "Liquid" | slice: 2, 5 }}
quid
{{ "Liquid" | slice: -3, 2 }}
ui

split

Divides an input string into an array using the argument as a separator. split is commonly used to convert comma-separated items from a string to an array.

分割字符串組成一個數組。

{% assign beatles = "John, Paul, George, Ringo" | split: ", " %}

{% for member in beatles %}
  {{ member }}
{% endfor %}


  John

  Paul

  George

  Ringo

固然這裏沒有列舉完全部的filter, 這些是相對比較經常使用的，記着這些，若是知足不了需求，再去官方文檔上翻閱翻閱。

博客原文：http://huangyanxiang.com/2017/09/20/jekyll-with-liquid.html