# Logic/conditional statements

Logic helpers allow you to place conditional requirements in Handlebars expressions.

Logic statements can use one or more of these properties to evaluate a condition: 

* `value` — A literal string or number (e.g. "Hello" or 3)
* `attribute` — The string ID/Name of a user-specific data
* `expression` — A helper that can use other helpers, attributes, and values to return a value

## If/Else

`if`, `else`, `else if` — If/else statements can conditionally render blocks of content. *If* and *else if* statements render content when the condition is true, and *else* renders content when all previous conditions in a [block expression](https://www.airship.com/docs/guides/personalization/handlebars/basics/#block-expressions) are false.

Use `if` explicitly to test that a variable exists, is not empty, or is not 0. Otherwise, any condition that evaluates a variable acts as an implicit *if* statement.

For example, you must explicitly declare `if` when testing whether or not the `fav_movie` variable exists, is not empty, and is not 0.

```text
{{#if fav_movie}}
   Your favorite movie is {{fav_movie}}.
{{else}}
   Maybe you'd enjoy a book instead.
{{/if}}
```


When testing the value of the `fav_movie` variable, you can use other logic helpers such as [Equal](#equal) and combine them with else statements.

```text
{{#eq fav_movie "Indiana Jones"}}Did you like The Last Crusade or Temple of Doom?
{{else eq fav_movie "Star Wars"}}Are you into the OG trilogy or are you a prequel person?
{{else}}What's your favorite book?{{/eq}}
```


You can chain multiple `else` statements — similar to *else if* statements in other languages — to test a series of variables. Generally, the last `else` statement contains no parameters and determines what happens if all previous conditions fail.

## And/Or

`and`, `or` — These operators help you string together complex conditions to show the right content to the right members of your audience.

> **Note:** `and` renders a block of content if **all** conditions are true.
> 
> `or` renders a block of content if **any** of the conditions are true.


|  Format   |  Example  |  Output  |
|---|---|---|
| `{{#and expression expression}}`  | `{{#and (eq genre "action") (eq era "80s") }}<br/>You will definitely like Indiana Jones!<br/>{{/and}}`  | If **all** conditions are true, "You will definitely like Indiana Jones!" will display  |
| `{{#or expression expression}}`  | `{{#or (eq genre "action") (eq era "80s") }}<br/>You might be interested in Indiana Jones.<br/>{{/or}}`  | If **any** conditions are true, "You might be interested in Indiana Jones.  will display  |

## Equal

`eq` — Equality operators let you test the value of a merge field or the result of an expression — whether it is equal to, or not equal to, specific value. 

> **Tip:** Equality operators work well with both numeric or string (text) values. But cannot compare between the two value types.


In this example, the message is different if the `category` merge field contains the value `Accessories`:

```text
{{#eq category "Accessories"}}
   Enjoy up to $25 off!
{{else}}
   Get up to $75 off!
{{/eq}}
```


|  Format   |  Example  |  Output  |
|---|---|---|
| `{{#eq ## Equal

`eq` — Equality operators let you test the value of a merge field or the result of an expression — whether it is equal to, or not equal to, specific value. 

> **Tip:** Equality operators work well with both numeric or string (text) values. But cannot compare between the two value types.


In this example, the message is different if the `category` merge field contains the value `Accessories`:

```text
{{#eq category "Accessories"}}
   Enjoy up to $25 off!
{{else}}
   Get up to $75 off!
{{/eq}}
```


|  Format   |  Example  |  Output  |
|---|---|---|
| `{{#eq expression expression}}`  | `{{#eq quantity 2}}You have 2 items in your cart{{/eq}}`  | Displays text if `quantity` is equal to `2` |

## Not equal

`neq` — Renders content when a merge field or the result of an expression is *not* equal to a value.

|  Format   |  Example  |  Output  |
|---|---|---|
| `{{#neq expression expression}}`  | `{{#neq movie "Looper"}}You answered incorrectly. The correct answer is Looper{{/neq}}`  | Display text if `movie` does not equal `Looper` |

## Not

`not` — Renders content if a merge field or the result of an expression does not exist, is empty, is false, or is 0. This is a direct way to test for the availability of a merge field.

|  Format   |  Example  |  Output  |
|---|---|---|
| `{{#not expression}}`  | `{{#not watch_queue}}Your queue is empty, add a show to watch.{{/not}}`  | If `watch_queue` is empty or 0, "Your queue is empty, add a show to watch."  will display |

## Unless

`unless` — Renders content in a template if a condition is false — like a reverse `if` condition. You might want to use `unless` when you only really need the `else` statement for a condition.

|  Format   |  Example  |  Output  |
|---|---|---|
| `{{#unless expression}}`  | `{{#unless dislikes_indiana_jones}}You'll probably like Indiana Jones{{/unless}}`  |  Airship will render message content if the condition `dislikes_indiana_jones` is empty or false. |

## Greater than and Less than

`gt`, `lt`, `gte`, `lte` — Use the following operators to show content if the value of a variable — or the length of an array — is greater than, less than, greater than or equals, or less than or equals a particular value.

> **Tip:** These operators are for numerical values only.


|  Format   |  Example  |  Output  |
|---|---|---|
| `{{#gt expression}}`  | `{{#gt quantity 2}}You have more than 2 items in your cart{{/gt}}`  | Displays text if `quantity` is greater than `2` |
| `{{#lt expression}}`  | `{{#lt quantity 2}}You have less than 2 items in your cart{{/lt}}` | Displays text if `quantity` is less than `2` |
| `{{#gte expression}}`  | `{{#gte quantity 2}}You have enough items in your cart to unlock our discount{{/gte}}`  | Displays text if `quantity` is greater than or equal to `2` |
| `{{#lte expression}}`  | `{{#lte quantity 2}}You don't have enough items in your cart to unlock our discount{{/lte}}` | Displays text if `quantity` is less than or equal to `2` |

> **Note:** Array lengths are 0-indexed. For example, if an array has 3 entries, `{{#gte field.length 2}}` will be true.