From a239a30ed41c30cb49903d817cb4e52b0f499900 Mon Sep 17 00:00:00 2001
From: patrick brisbin <pbrisbin@gmail.com>
Date: Wed, 12 Jun 2019 10:15:38 -0400
Subject: [PATCH 1/2] Only set unset variables

---
 src/LoadEnv.hs      | 12 +++++++++---
 test/LoadEnvSpec.hs |  9 +++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/LoadEnv.hs b/src/LoadEnv.hs
index 25e2bdb..19254e8 100644
--- a/src/LoadEnv.hs
+++ b/src/LoadEnv.hs
@@ -23,14 +23,15 @@ module LoadEnv
     , loadEnvFromAbsolute
     ) where
 
-import Control.Monad ((<=<))
+import Control.Monad (unless, (<=<))
 import Data.Bool (bool)
 import Data.Foldable (for_, traverse_)
 import Data.List (inits)
+import Data.Maybe (isJust)
 import LoadEnv.Parse
 import System.Directory
     (doesFileExist, findFile, getCurrentDirectory, makeAbsolute)
-import System.Environment (setEnv)
+import System.Environment (lookupEnv, setEnv)
 import System.FilePath (isRelative, joinPath, splitDirectories)
 import Text.Parsec.String (parseFromFile)
 
@@ -63,7 +64,12 @@ loadEnvFrom name = do
 
     for_ mFile $ \file -> do
         result <- parseFromFile parseEnvironment file
-        either print (traverse_ $ uncurry setEnv) result
+        either print (traverse_ $ uncurry defaultEnv) result
+
+defaultEnv :: String -> String -> IO ()
+defaultEnv k v = do
+    exists <- isJust <$> lookupEnv k
+    unless exists $ setEnv k v
 
 -- | @'loadEnvFrom'@, but don't traverse up the directory tree
 loadEnvFromAbsolute :: FilePath -> IO ()
diff --git a/test/LoadEnvSpec.hs b/test/LoadEnvSpec.hs
index 5c12ee0..cc6bdf1 100644
--- a/test/LoadEnvSpec.hs
+++ b/test/LoadEnvSpec.hs
@@ -25,6 +25,15 @@ spec = after_ cleanup $ do
             mbar `shouldBe` Just "bar"
             mbat `shouldBe` Just "bat"
 
+        it "does not override pre-existing variables" $ do
+            writeFile envFile $ unlines ["FOO=bar"]
+            setEnv "FOO" "baz"
+
+            loadEnvFrom envFile
+
+            mbar <- lookupEnv "FOO"
+            mbar `shouldBe` Just "baz"
+
         it "does not fail if the file is not present" $ do
             loadEnvFrom "i-do-not-exist"
 

From 179ce2d51e8f5227b90cc985be4c98b995a0f203 Mon Sep 17 00:00:00 2001
From: patrick brisbin <pbrisbin@gmail.com>
Date: Wed, 12 Jun 2019 10:27:57 -0400
Subject: [PATCH 2/2] Version bump

---
 CHANGELOG.md | 25 ++++++++++++++++++++++++-
 package.yaml |  2 +-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e7d408f..f63dcb6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,30 @@
-## [*Unreleased*](https://github.com/pbrisbin/load-env/compare/v0.2.0.2...master)
+## [*Unreleased*](https://github.com/pbrisbin/load-env/compare/v0.2.1.0...master)
 
 None
 
+## [v0.2.1.0](https://github.com/pbrisbin/load-env/compare/v0.2.0.2...v0.2.1.0)
+
+- Don't override values already set in the environment
+
+  Given a hypothetical program `load-env`, which uses one of our `loadEnv`
+  functions on `stdin`:
+
+  Previously,
+
+  ```
+  FOO=bar load-env <<EOM
+  FOO=bat
+  EOM
+  ```
+
+  would override `FOO` to `bat` when `load-env` ran. But now, it will see `FOO`
+  is already `bar` and leave it.
+
+  This is better behavior under the assumption that a `.env` file is meant to
+  specify *defaults* in the case of nothing explicit. When there are explicit
+  values in the environment, it's most likely that our user indeed wants them
+  respected.
+
 ## [v0.2.0.2](https://github.com/pbrisbin/load-env/compare/v0.2.0.1...v0.2.0.2)
 
 - Allow lower-case characters in variable names [@denibertovic](https://github.com/pbrisbin/load-env/pull/4)
diff --git a/package.yaml b/package.yaml
index da1df3d..f0da3d7 100644
--- a/package.yaml
+++ b/package.yaml
@@ -1,6 +1,6 @@
 ---
 name: load-env
-version: '0.2.0.2'
+version: '0.2.1.0'
 synopsis: Load environment variables from a file.
 description: >
   Parse a .env file and load any declared variables into the current process's