operators.md

Operators

An operator is a statement that evaluates some code, and makes a decision about what to do next. Operators can be used for comparing two values, inspecting a single value, or evaluating whether or not some code returns true.

{% hint style="info" %} For further discussion on how Liquid treats values, see their documentation: Truthiness and falsiness in Liquid. {% endhint %}

Comparison operators

If b = 6, the table below illustrates the comparison operators and the way they interact with b:

Operator	Description	Example	Result
==	equal to	b == 6	true
!=	not equal	b != 6	false
>	greater than	b > 5	true
<	less than	b < 6	false
>=	greater than or equal to	b >= 6	true
<=	less than or equal to	b <= 6	true

Examples

{% assign order_qualifies = false %}

{% if order.cancelled_at == blank and cancel_risk %}
  {% assign order_qualifies = true %}
{% endif %}

{% if has_product != true %}
  {% log "Order has no products; skipping" %}
  {% assign send_email = false %}
{% endif %}

Testing for blank, empty

Liquid supports equality/inequality testing a value against blank or empty. In this way, Liquid allows the author to ask, "is this value blank?", or "is this value empty?"

Blank

Quoting from the Rails API:

An object is blank if it's false, empty, or a whitespace string. For example, nil, '', ' ', [], {}, and false are all blank.

{% assign empty_string = "" %}
{% assign whitespace_string = "  " %}
{% assign non_blank_string = "  !!  " %}
{% assign non_empty_array = "1,2,3" | split: "," %}
{% assign empty_hash = hash %}

{% comment %}
  The following `if` statements all pass.
{% endcomment %}
{% if empty_string == blank %}
{% if whitespace_string == blank %}
{% if non_blank_string != blank %}
{% if non_empty_array != blank %}
{% if empty_hash == blank %}

Empty

An array, hash, or string can be tested for emptiness. An array is empty if it has no elements; a hash is empty if it has no key-value pairs; a string is empty if its length is zero.

{% hint style="info" %} A string that only contains whitespace is not empty, but it is blank! {% endhint %}

{% assign empty_string = "" %}
{% assign whitespace_string = "  " %}
{% assign non_blank_string = "  !!  " %}
{% assign non_empty_array = "1,2,3" | split: "," %}
{% assign empty_hash = hash %}

{% comment %}
  The following `if` statements all pass.
{% endcomment %}
{% if empty_string == empty %}
{% if whitespace_string != empty %}
{% if non_blank_string != empty %}
{% if non_empty_array != empty %}
{% if empty_hash == empty %}

Contains operator

The contains operator is used to check for the existence of a substring in a string, or for a specific element in an array.

Substring containment

{% if email_domain contains "@" %}
  {% error "Do not include '@' symbols in email domains. Thanks!" %}
{% endif %}

Array element containment

{% assign product_tags = "foo, bar, baz" | split: ", " %}
{% assign product_is_tagged_bar = false %}

{% if product_tags contains "bar" %}
  {% assign product_is_tagged_bar = true %}
{% endif %}

Logical operators

Liquid has two logical operators: and and or.

If b = 3 and c = 6, the table below illustrates the logical operators in Liquid, and the way they interact with b and b:

Operator	Example	Result
and	b < 2 and c < 6	false
or	b < 2 or c < 6	true

Check if both the shipping address and billing are blank

{% if order.shipping_address != blank and order.billing_address != blank %}
  {% comment %} do something {% endcomment %}
{% endif %}

Check if tag equals blank or a customer's tags contains a certain tag

{% if tag == blank or customer.tags contains tag %}
  {% comment %} do something {% endcomment %}
{% endif %}