Example of Package.swift with environment variables support

Package.swift

// swift-tools-version:4.0
import PackageDescription

#if os(Linux)
import Glibc
#else
import Darwin.C
#endif

enum Enviroment: String {
	static let `default`: Enviroment = .development

	case development, production
	
	static func get() -> Enviroment {
		if let envPointer = getenv("ENV_TYPE") {
			let env = String(cString: envPointer)
			return Enviroment(rawValue: env) ?? .default
		} else {
			return .default
		}
	}
}

var dependencies: [Package.Dependency] = [
	.package(url: "https://github.com/vapor/vapor.git", from: "3.1.0"),
	.package(url: "https://github.com/Sorix/whirr-feedback-api-model", .branch("develop"))
]

var appTargetDependencies: [Target.Dependency] = ["Vapor", "FluentSQLite", "APIModel", "GooglePlaces"]

switch Enviroment.get() {
case .production:
	dependencies.append(.package(url: "https://github.com/vapor/fluent-postgresql.git", from: "1.0.0"))
	appTargetDependencies.append("FluentPostgreSQL")
case .development:
	dependencies.append(.package(url: "https://github.com/vapor/fluent-sqlite.git", from: "3.0.0"))
	appTargetDependencies.append("FluentSQLite")
}

let package = Package(
    name: "backend",
    dependencies: dependencies,
    targets: [
        .target(name: "GooglePlaces", dependencies: ["Vapor"]),
        .target(name: "App", dependencies: appTargetDependencies),
        .target(name: "Run", dependencies: ["App"]),
        .testTarget(name: "AppTests", dependencies: ["App"])
    ]
)