Add Env with default value

os/env.go

@@ -0,0 +1,18 @@
+//go:build go1.18
+// +build go1.18
+
+package osext
+
+import "os"
+
+// Env retrieves the value of the environment variable named by the key.
+// If the variable is present in the environment, its value (which may be empty) is returned.
+// Otherwise, the provided defaultValue is returned.
+// The function is generic and can return any type T, but the caller must ensure that
+// the type assertion is valid for the expected type of the environment variable.
+func Env[T any](key string, defaultValue T) T {
+	if v, ok := os.LookupEnv(key); ok {
+		return any(v).(T)
+	}
+	return defaultValue
+}

os/env_test.go

@@ -0,0 +1,22 @@
+//go:build go1.18
+// +build go1.18
+
+package osext
+
+import (
+	"os"
+	"testing"
+
+	. "github.com/go-playground/assert/v2"
+)
+
+func TestEnv(t *testing.T) {
+	key := "ENV_FOO"
+	os.Setenv(key, "FOO")
+	defer os.Clearenv()
+
+	Equal(t, "FOO", Env(key, "default_value"))
+
+	os.Unsetenv(key)
+	Equal(t, "default_value", Env(key, "default_value"))
+}