Control Flow Tags

Control Flow tags determine which block of code should be executed based on different conditions.

1. if
2. elsif / else
3. case / when
4. unless

if

Executes a block of code only if a certain condition is met.

Input

  {% if rental.title == 'Apartment 051' %}
      This Apartment comes with a swimming pool.
  {% endif %}

Output

  This Apartment comes with a swimming pool.

elsif / else

Adds more conditions within an if or unless block.

Input

<!-- If customer.name = 'anonymous' -->

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

Output

  Hey Anonymous!

case / when

Creates a switch statement to compare a variable with different values. case initializes the switch statement, and when compares its values.

Input

  {% assign handle = 'Apartment 4129' %}
  {% case handle %}
    {% when 'Apartment 4129' %}
       It is an Apartment 4129
    {% when 'Apartment 5100' %}
       It is an Apartment 5100
    {% else %}
       This is not an Apartment 4129 nor a Apartment 5100
  {% endcase %}

Output

  It is an Apartment 4129

unless

Similar to if, but executes a block of code only if a certain condition is not met.

Input

  {% unless rental.title == 'Apartment 051' %}
      This Apartment is without a swimming pool.
  {% endunless %}

Output

  This Apartment is without a swimming pool.

This would be the equivalent of doing the following:

  {% if rental.title != 'Apartment 051' %}
      This Apartment is without a swimming pool.
  {% endif %}