diff --git a/examples/basic/build.gradle.kts b/examples/basic/build.gradle.kts
index ff5b1b9..d131d1f 100644
--- a/examples/basic/build.gradle.kts
+++ b/examples/basic/build.gradle.kts
@@ -11,3 +11,6 @@ try {
     println("example print: ${e.message}")
 }
 println(env.QUX.value)
+
+// All environment variables which are merged with variables specified in .env files.
+env.allVariables
diff --git a/examples/basic/settings.gradle.kts b/examples/basic/settings.gradle.kts
index 7ebc927..6e33b56 100644
--- a/examples/basic/settings.gradle.kts
+++ b/examples/basic/settings.gradle.kts
@@ -1,7 +1,7 @@
 pluginManagement {
     repositories {
-        gradlePluginPortal()
         mavenLocal()
+        gradlePluginPortal()
     }
 }
 
diff --git a/examples/basic/sub/build.gradle.kts b/examples/basic/sub/build.gradle.kts
index c6ae2da..47ff8f9 100644
--- a/examples/basic/sub/build.gradle.kts
+++ b/examples/basic/sub/build.gradle.kts
@@ -6,3 +6,6 @@ try {
     println("[$name] example print: ${e.message}")
 }
 println("""[$name] ${env.QUX.value}""")
+
+// All environment variables which are merged with variables specified in .env files.
+env.allVariables
diff --git a/plugin/src/main/kotlin/co/uzzu/dotenv/EnvProviders.kt b/plugin/src/main/kotlin/co/uzzu/dotenv/EnvProviders.kt
index 53335ff..0198c32 100644
--- a/plugin/src/main/kotlin/co/uzzu/dotenv/EnvProviders.kt
+++ b/plugin/src/main/kotlin/co/uzzu/dotenv/EnvProviders.kt
@@ -20,5 +20,5 @@ interface EnvProvider {
  */
 class SystemEnvProvider : EnvProvider {
     override fun getenv(name: String): String? = System.getenv(name)
-    override fun getenv(): Map<String, String> = System.getenv()
+    override fun getenv(): Map<String, String> = System.getenv().filterValues { it != null }
 }
diff --git a/plugin/src/main/kotlin/co/uzzu/dotenv/gradle/DotEnvProperties.kt b/plugin/src/main/kotlin/co/uzzu/dotenv/gradle/DotEnvProperties.kt
index 864f5bb..02171ec 100644
--- a/plugin/src/main/kotlin/co/uzzu/dotenv/gradle/DotEnvProperties.kt
+++ b/plugin/src/main/kotlin/co/uzzu/dotenv/gradle/DotEnvProperties.kt
@@ -2,16 +2,33 @@ package co.uzzu.dotenv.gradle
 
 import co.uzzu.dotenv.EnvProvider
 
+/**
+ * This object will be added as extension which named "env" to the Project.
+ */
 open class DotEnvRoot(
     private val envProvider: EnvProvider,
-    private val map: Map<String, String>
+    private val dotenvMap: Map<String, String?>
 ) {
+    /**
+     * @return All environment variables which are merged with variables specified in .env files.
+     */
+    val allVariables: Map<String, String>
+        get() {
+            val results = envProvider.getenv().toMutableMap()
+            dotenvMap.forEach { (key, value) ->
+                if (value != null && results[key] == null) {
+                    results[key] = value
+                }
+            }
+            return results.toMap()
+        }
+
     /**
      * @return Indicates an environment variable with specified name is present
      */
     fun isPresent(name: String): Boolean =
         envProvider.getenv()[name]?.let { true }
-            ?: map[name]?.let { true }
+            ?: dotenvMap[name]?.let { true }
             ?: false
 
     /**
@@ -20,7 +37,7 @@ open class DotEnvRoot(
      */
     fun fetch(name: String) =
         envProvider.getenv()[name]
-            ?: map[name]
+            ?: dotenvMap[name]
             ?: throw IllegalStateException("""Environment variable $name was not set.""")
 
     /**
@@ -29,7 +46,7 @@ open class DotEnvRoot(
      */
     fun fetch(name: String, defaultValue: String) =
         envProvider.getenv()[name]
-            ?: map[name]
+            ?: dotenvMap[name]
             ?: defaultValue
 
     /**
@@ -37,9 +54,13 @@ open class DotEnvRoot(
      */
     fun fetchOrNull(name: String): String? =
         envProvider.getenv()[name]
-            ?: map[name]
+            ?: dotenvMap[name]
 }
 
+/**
+ * This object has environment variables defined on .env file.
+ * This object will be added as extension which named environment variable name, to the DotEnv object.
+ */
 open class DotEnvProperty(
     private val envProvider: EnvProvider,
     private val name: String,
diff --git a/plugin/src/test/kotlin/co/uzzu/dotenv/gradle/DotEnvRootTest.kt b/plugin/src/test/kotlin/co/uzzu/dotenv/gradle/DotEnvRootTest.kt
index 371dca9..7505281 100644
--- a/plugin/src/test/kotlin/co/uzzu/dotenv/gradle/DotEnvRootTest.kt
+++ b/plugin/src/test/kotlin/co/uzzu/dotenv/gradle/DotEnvRootTest.kt
@@ -7,9 +7,9 @@ import org.junit.jupiter.api.Assertions.assertNull
 import org.junit.jupiter.api.Assertions.assertThrows
 import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertAll
 
 class DotEnvRootTest {
-
     @Test
     fun isPresentByEnv() {
         val envProvider = InMemoryEnvProvider(mapOf("FOO" to "env"))
@@ -93,4 +93,32 @@ class DotEnvRootTest {
         val root = DotEnvRoot(envProvider, mapOf())
         assertNull(root.fetchOrNull("FOO"))
     }
+
+    @Test
+    fun allVariables() {
+        val envProvider = InMemoryEnvProvider(
+            mapOf(
+                "FOO" to "env",
+                "BAR" to "env"
+            )
+        )
+        val root = DotEnvRoot(
+            envProvider,
+            mapOf(
+                "BAR" to "dotenv",
+                "BAZ" to "dotenv",
+                "QUX" to "dotenv",
+                "QUUX" to null
+            )
+        )
+        val allVariables = root.allVariables
+        assertAll(
+            { assertEquals("env", allVariables["FOO"]) },
+            { assertEquals("env", allVariables["BAR"]) },
+            { assertEquals("dotenv", allVariables["BAZ"]) },
+            { assertEquals("dotenv", allVariables["QUX"]) },
+            { assertEquals(null, allVariables["QUUX"]) },
+            { assertEquals(null, allVariables["CORGE"]) }
+        )
+    }
 }