> For the complete documentation index, see [llms.txt](https://docs.intrepidcs.com/vspy-3-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.intrepidcs.com/vspy-3-documentation/vehicle-spy-main-menus/main-menu-scripting-and-automation/function-blocks/function-blocks-types/script-type-function-block-commands/script-type-function-block-command-set-value-if.md).

# Script Type Function Block Command: Set Value If

### Command Description

The **Set Value If** command combines the [If](/vspy-3-documentation/vehicle-spy-main-menus/main-menu-scripting-and-automation/function-blocks/function-blocks-types/script-type-function-block-commands/script-type-function-block-commands-if-else-else-if-end-if.md) and [Set Value](/vspy-3-documentation/vehicle-spy-main-menus/main-menu-scripting-and-automation/function-blocks/function-blocks-types/script-type-function-block-commands/script-type-function-block-command-set-value.md) commands in a special way. An expression is evaluated, as it would be in an **If** command, and then the following happens based on the result:

* **Expression is True:** The **Set Value** statement is executed, and then the commands following the **Set Value If** are *also* executed, just as would have occurred if this had been a normal **If** statement that evaluated as **True**.
* **Expression is False:** The **Set Value** statement is *not* executed, and all the following commands are skipped until the next **Else**, **Else If** or **End If** statement is seen, just as if this had been a normal **If** statement that evaluated as **False**.

From a logical standpoint, then, there is no difference between one **Set Value If** command and separate **If** and **Set Value** commands. In Figure 1, Steps 1 to 5 and Steps 7 to 10 do basically the same thing.

![Figure 1: The same script using separate If and Set Value commands (steps 1 to 5) and the Set Value If command (steps 7 to 10).](https://3170208387-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FL6lcovCpkhoS9uTOFtEp%2Fuploads%2FEiuzxzsTIPd8jSNrpAuq%2Ffb_set_value_if_1.gif?alt=media\&token=01e07f09-396e-4289-bb4a-3a1af9764566)

However, there is *one important difference:* the **Set Value If**command guarantees that the **If** part of the command and the **Set Value** part will be executed *atomically.* This means that they are executed together, and it is guaranteed that if the expression is **True**, no signal values will change before the assignment operation takes place.

The script in Figure 1 checks if an application signal called **User Input Value**is positive in step 1, and if so, assigns it to a transmit message signal in step 2 before sending the message. The intent, then, is only to send the data if**User Input Value** is positive. It is possible, however, that this value might have changed between these two steps (perhaps by a differentfunction block script) which could result in transmitting the message with a negative value. Using a **Set Value If** statement instead, as in step 7, ensures that this will not happen.

Note that the same rules for combining an **If** statement with the [Else](/vspy-3-documentation/vehicle-spy-main-menus/main-menu-scripting-and-automation/function-blocks/function-blocks-types/script-type-function-block-commands/script-type-function-block-commands-if-else-else-if-end-if.md), [Else If and End If](/vspy-3-documentation/vehicle-spy-main-menus/main-menu-scripting-and-automation/function-blocks/function-blocks-types/script-type-function-block-commands/script-type-function-block-commands-if-else-else-if-end-if.md) commands also apply to **Set Value If.** You must have an **End If** to match each **Set Value If**. The use of **Else** and **Else If** is optional, and if present, they are used in the same way as with an **If** statement.

### Value Field Parameters

Double-click the **Value** field for the command to launch a specialized window for it, where you can enter both the evaluation (**If**) expression and assignment (**Set Value**) expression using the [Expression Builder](/vspy-3-documentation/shared-features-in-vehicle-spy/shared-features-expression-builder.md). Figure 2 shows this window illustrating the expressions used for the command in step 7 of Figure 1.

![Figure 2: Setup window for the Set Value If command.](https://3170208387-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FL6lcovCpkhoS9uTOFtEp%2Fuploads%2Fh9VFztwWe3S647IC2Fjc%2Ffb_set_value_if_2.gif?alt=media\&token=dce88950-867b-4718-8a7b-c30ceb0d2fb7)


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.intrepidcs.com/vspy-3-documentation/vehicle-spy-main-menus/main-menu-scripting-and-automation/function-blocks/function-blocks-types/script-type-function-block-commands/script-type-function-block-command-set-value-if.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.