# Dynamic configuration {#dynamic-configuration}

There are certain scenarios where you might need to dynamically configure your
project at generation time. For example, you might want to change the name of
the app, the bundle identifier, or the deployment target based on the
environment where the project is being generated. Tuist supports that via
environment variables, which can be accessed from the manifest files.

## Configuration through environment variables {#configuration-through-environment-variables}

Tuist allows passing configuration through environment variables that can be
accessed from the manifest files. For example:

```bash
TUIST_APP_NAME=MyApp tuist generate
```

If you want to pass multiple environment variables just separate them with a
space. For example:

```bash
TUIST_APP_NAME=MyApp TUIST_APP_LOCALE=pl tuist generate
```

## Reading the environment variables from manifests {#reading-the-environment-variables-from-manifests}

Variables can be accessed using the
<LocalizedLink href="/references/project-description/enums/environment">`Environment`</LocalizedLink>
type. Any variables following the convention `TUIST_XXX` defined in the
environment or passed to Tuist when running commands will be accessible using
the `Environment` type. The following example shows how we access the
`TUIST_APP_NAME` variable:

```swift
func appName() -> String {
    if case let .string(environmentAppName) = Environment.appName {
        return environmentAppName
    } else {
        return "MyApp"
    }
}
```

Accessing variables returns an instance of type `Environment.Value?` which can
take any of the following values:

| Case              | Description                                 |
| ----------------- | ------------------------------------------- |
| `.string(String)` | Used when the variable represents a string. |

You can also retrieve the string or boolean `Environment` variable using either
of the helper methods defined below, these methods require a default value to be
passed to ensure the user gets consistent results each time. This avoids the
need to define the function appName() defined above.

::: code-group

```swift [String]
Environment.appName.getString(default: "TuistServer")
```

```swift [Boolean]
Environment.isCI.getBoolean(default: false)
```
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:::