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Environment Variables

Environment variables allow you to configure device-specific settings without changing your code. Each device can have different values for the same variables, making it easy to customize behavior across your fleet.

Defining Environment Variables​

To add environment variables to your app, define a JSON Schema in your release configuration. This is done by setting envSchema and optionally envUiSchema when publishing your app.

envSchema​

The envSchema defines what environment variables your app accepts using JSON Schema:

{
  "type": "object",
  "required": ["pinNumber"],
  "properties": {
    "pinNumber": {
      "title": "Pin number",
      "type": "string"
    }
  }
}

envUiSchema​

The envUiSchema customizes how the form is rendered using React JSON Schema Form UI Schema:

{
  "pinNumber": {
    "ui:placeholder": "Enter GPIO pin number"
  }
}

Setting Values​

When adding a new device to your app, the environment variables form appears during device setup. Users can configure values specific to each device before flashing.

Accessing Environment Variables in Code​

Environment variables are available through the standard WASI environment interface:

#include <stdlib.h>

int main() {
    char* pin_number = getenv("pinNumber");

    if (pin_number) {
        int pin = atoi(pin_number);
        // Use the pin value
    }

    return 0;
}