An operator makes comparisons between two values in an expression.

Assignment

As you've seen with the set command, a single = (equals) character assigns a value to a variable:

{% set this = 0 %}
{% set that = 1 %}
this is {{this}} and that is {{that}}

this is 0 and that is 1

Equals

To check if a variable is equal to a specific value, use two equal signs (==):

{% set this = 1 %}
{% set that = 1 %}
{% if this == that %}
This and that are equal.
{% endif -%}

This and that are equal.

To check that a variable isn't equal to a specific value, use !=:

{% set this = 0 %}
{% set that = 1 %}
{% if this != that %}
This doesn't equal that.
{% endif -%}

This doesn't equal that.

To check if one variable is less than another, use < or <=:

{% set little = 5 %}
{% set big = 1000 %}
{% if little < big %}
{{little}} is less than {{big}}
{% endif -%}

5 is less than 1000

To check if one variable is greater than another, use > or >=:

{% set little = 5 %}
{% set big = 1000 %}
{% if big > little %}
{{big}} is greater than {{little}}
{% endif -%}

1000 is greater than 5

You can check if a value exists in a list by using the in test:

{% set colors = ['blue','green','red'] %}
{% if 'red' in colors %}
One of the colors is red.
{% endif -%}

One of the colors is red.

You can also negate that test with not in:

{% set colors = ['blue','green','red'] %}
{% if 'orange' not in colors %}
Orange is not one of the colors.
{% endif -%}

Orange is not one of the colors.