From cc6b967e0802ba33306274b5a9ac67eb13721041 Mon Sep 17 00:00:00 2001
From: Matthias Simon <5nord@users.noreply.github.com>
Date: Mon, 25 Apr 2022 04:21:01 +0200
Subject: [PATCH] Prefer environment variables over local variables (#12)

Closes #11
---
 fixtures/vars.env |  5 +++++
 gotenv.go         |  4 ++++
 gotenv_test.go    | 16 ++++++++++++++++
 3 files changed, 25 insertions(+)
 create mode 100644 fixtures/vars.env

diff --git a/fixtures/vars.env b/fixtures/vars.env
new file mode 100644
index 0000000..043d34f
--- /dev/null
+++ b/fixtures/vars.env
@@ -0,0 +1,5 @@
+A="fromFile"
+B="$A"
+
+D="$C"
+C="fromFile"
diff --git a/gotenv.go b/gotenv.go
index 5f062e5..55c17ab 100644
--- a/gotenv.go
+++ b/gotenv.go
@@ -220,6 +220,10 @@ func varReplacement(s string, hsq bool, env Env) string {
 
 	v := mn[3]
 
+	if replace, ok := os.LookupEnv(v); ok {
+		return replace
+	}
+
 	replace, ok := env[v]
 	if !ok {
 		replace = os.Getenv(v)
diff --git a/gotenv_test.go b/gotenv_test.go
index a289bc6..490e86a 100644
--- a/gotenv_test.go
+++ b/gotenv_test.go
@@ -243,6 +243,22 @@ func TestLoad_overriding(t *testing.T) {
 	os.Clearenv()
 }
 
+func TestLoad_overrideVars(t *testing.T) {
+	os.Setenv("A", "fromEnv")
+	err := gotenv.Load("fixtures/vars.env")
+	assert.Nil(t, err)
+	assert.Equal(t, "fromEnv", os.Getenv("B"))
+	os.Clearenv()
+}
+
+func TestLoad_overrideVars2(t *testing.T) {
+	os.Setenv("C", "fromEnv")
+	err := gotenv.Load("fixtures/vars.env")
+	assert.Nil(t, err)
+	assert.Equal(t, "fromEnv", os.Getenv("D"))
+	os.Clearenv()
+}
+
 func TestLoad_Env(t *testing.T) {
 	err := gotenv.Load(".env.invalid")
 	assert.NotNil(t, err)