Liquid - Tags: Flow Control

If / Else

if / else statements should be familiar from other programming languages. Liquid implements them with the following tags:

• {% if <CONDITION> %} ... {% endif %}: Encloses a section of a template which will only be run if the condition is true.
• {% elsif <CONDITION> %}: Can optionally be used within an if ... endif block. Specifies another condition; if the initial "if" fails, Liquid tries the "elsif", and runs the following section of the template if it succeeds. You can use any number of elsifs in an if block.
• {% else %}: Can optionally be used within an if ... endif block, after any "elsif" tags. If all preceding conditions fail, Liquid will run the section of template following the "else" tag.
• {% unless <CONDITION> %} ... {% endunless %}: The reverse of an "if" statement. Don't use "elsif" or "else" with an unless statement.

The condition of an if, elsif, or unless tag should be either a normal Liquid expression or a comparison using Liquid expressions.
Note that the comparison operators are implemented by the "if"-like tags; they don't work anywhere else in Liquid.

Operators

The available comparison operators are:

• ==, !=, and <>: equality and inequality (the latter two are synonyms)
• <, <=, >, >=: less/greater-than
• There are also special values empty and blank (unquoted) that you can compare arrays to; the comparison is true if the array has no members.
• contains: similar to Ruby's include? method, implemented on strings, arrays, and hashes. If the left argument is a string and the right isn't, it stringifies the right.

Always be mindful of the Liquid syntax. For example, {% if rs.enabled == 'true' %} will work while {% if rs.enabled=='true' %} (without the spaces) will not.

Boolean operators

The available Boolean operators are:

• and
• or

You can use the and and or operators to include more than one condition in a control flow tag. and and or can be chained together to create complex conditionals.

If you use multiple and or or operators, note that and operators will be evaluated first, then or operators. You cannot use parentheses to simulate an order of operations and control the order of operator evaluation. Parentheses are invalid characters within Liquid tags and prevent your tags from working.

and

The and operator lets you add additional conditions to a tag. A condition with an and will only be true if both the left and the right side of the condition are true.

Input

{% if line_item.grams > 20000 and customer_address.city == 'Ottawa' %}
  You're buying a heavy item, and are in the same city as our store. Choose local pick-up as a shipping option to avoid paying high shipping costs.
{% endif %}

Output

You're buying a heavy item, and are in the same city as our store. Choose local pick-up as a shipping option to avoid paying high shipping costs.

or

The or operator lets you add additional conditions to a tag. A condition with an or will be true if either the left or the right side of the condition is true.

{% if customer.tags contains 'VIP' or customer.email contains 'mycompany.com' %}
  Welcome! We're pleased to offer you a special discount of 15% on all products.
{% else %}
  Welcome to our store!
{% endif %}

Output

Welcome! We're pleased to offer you a special discount of 15% on all products.

Types and truthiness

Truthiness summary table

Liquid expressions are tested for "truthiness" in a Ruby-like way:

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

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

{% comment %} Same as above {% endcomment %}
{% if user != null %}
  Hello {{ user.name }}
{% endif %}

{% if user.name == 'tobi' %}
  Hello tobi
{% elsif user.name == 'bob' %}
  Hello bob
{% endif %}

{% if user.name == 'tobi' or user.name == 'bob' %}
  Hello tobi or bob
{% endif %}

{% if user.name == 'bob' and user.age > 45 %}
  Hello old bob
{% endif %}

{% if user.name != 'tobi' %}
  Hello non-tobi
{% endif %}

{% comment %} Same as above {% endcomment %}
{% unless user.name == 'tobi' %}
  Hello non-tobi
{% endunless %}


{% comment %} Check for the size of an array {% endcomment %}
{% if user.payments == empty %}
  you never paid !
{% endif %}

{% if user.payments.size > 0  %}
  you paid !
{% endif %}

{% if user.age > 18 %}
  Login here
{% else %}
  Sorry, you are too young
{% endif %}

{% comment %} array = 1,2,3 {% endcomment %}
{% if array contains 2 %}
  array includes 2
{% endif %}

{% comment %} string = 'hello world' {% endcomment %}
{% if string contains 'hello' %}
  string includes 'hello'
{% endif %}

Case Statement

If you need more conditions, you can use the case statement:

{% case condition %}
{% when 1 %}
  hit 1
{% when 2 or 3 %}
  hit 2 or 3
{% else %}
  ... else ...
{% endcase %}

Example

{% case template %}

{% when 'label' %}
  {{ label.title }}
{% when 'product' %}
  {{ product.vendor }} / {{ product.title }}
{% else %}
  {{ page_title }}
{% endcase %}