Add export for exporting to environment

Sources/DotEnvy/Load.swift

@@ -46,6 +46,16 @@ extension DotEnvironment.Override {
 }
 
 extension DotEnvironment {
+    /// Export the `DotEnvironment` values into the process environment.
+    ///
+    /// - Parameter overwrite: Indicates if the calculated value should overwrite any existing value
+    ///                        in the process environment.
+    public func export(overwrite: Bool = true) {
+        for value in self.merge() {
+            setenv(value.key, value.value, overwrite ? 1 : 0)
+        }
+    }
+
     /// Load the contents of a dotenv file into a dictionary.
     ///
     /// Defaults to loading `.env` from the current working directory. If the file does not exist, an

Tests/DotEnvyTests/ExportTests.swift

@@ -0,0 +1,32 @@
+@testable import DotEnvy
+import XCTest
+
+final class ExportTests: XCTestCase {
+    func testOverwrite() throws {
+        setenv("KEY1", "ENVVALUE1", 1)
+        let dotenv = try DotEnvironment.make(
+            source: """
+            KEY1=DOTENVVALUE1
+            KEY2=DOTENVVALUE2
+            """,
+            overrides: .none
+        )
+        dotenv.export(overwrite: true)
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY1"], "DOTENVVALUE1")
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY2"], "DOTENVVALUE2")
+    }
+
+    func testNoOverwrite() throws {
+        setenv("KEY1", "ENVVALUE1", 1)
+        let dotenv = try DotEnvironment.make(
+            source: """
+            KEY1=DOTENVVALUE1
+            KEY2=DOTENVVALUE2
+            """,
+            overrides: .none
+        )
+        dotenv.export(overwrite: false)
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY1"], "ENVVALUE1")
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY2"], "DOTENVVALUE2")
+    }
+}