diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,8 @@
 ## MASTER
+## Dotenv 0.5.1.0
+
+* Add support for command substitution on env vars.
+
 ## Dotenv 0.5.0.2
 
 * Set `.env` file as default file for environment variables.
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -59,6 +59,38 @@
 about this. Fortunately, there is already some work for this issue in
 [GHC Phabricator](https://phabricator.haskell.org/D3726).
 
+### Variable substitution
+
+In order to use compound env vars use the following sintax within your env vars
+${your_env_var}. For instance:
+
+```
+DATABASE=postgres://${USER}@localhost/database
+```
+ 
+Running it on the CLI:
+
+```
+$ dotenv "echo $DATABASE"
+postgres://myusername@localhost/database
+```
+
+### Command substitution
+
+In order to use the standard output of a command in your env vars use the following
+sintax $(your_command). For instance:
+
+```
+DATABASE=postgres://$(whoami)@localhost/database
+```
+ 
+Running it on the CLI:
+
+```
+$ dotenv "echo $DATABASE"
+postgres://myusername@localhost/database
+```
+
 ## Configuration
 
 The first argument to `loadFile` specifies whether you want to
diff --git a/dotenv.cabal b/dotenv.cabal
--- a/dotenv.cabal
+++ b/dotenv.cabal
@@ -1,5 +1,5 @@
 name:                dotenv
-version:             0.5.0.2
+version:             0.5.1.0
 synopsis:            Loads environment variables from dotenv files
 homepage:            https://github.com/stackbuilders/dotenv-hs
 description:
@@ -61,7 +61,7 @@
                        , dotenv
                        , optparse-applicative >=0.11 && < 0.15
                        , megaparsec >= 6.0 && < 7.0
-                       , process
+                       , process >= 1.4.3.0
                        , text
                        , transformers >=0.4 && < 0.6
   other-modules: Paths_dotenv
@@ -83,6 +83,7 @@
   build-depends:         base >=4.7 && <5.0
                        , base-compat >= 0.4
                        , megaparsec >= 6.0 && < 7.0
+                       , process >= 1.4.3.0
                        , text
                        , transformers >=0.4 && < 0.6
                        , exceptions >= 0.8 && < 0.9
@@ -116,6 +117,7 @@
                      , dotenv
                      , megaparsec >= 6.0 && < 7.0
                      , hspec
+                     , process >= 1.4.3.0
                      , text
                      , transformers >=0.4 && < 0.6
                      , exceptions >= 0.8 && < 0.9
diff --git a/spec/Configuration/Dotenv/ParseSpec.hs b/spec/Configuration/Dotenv/ParseSpec.hs
--- a/spec/Configuration/Dotenv/ParseSpec.hs
+++ b/spec/Configuration/Dotenv/ParseSpec.hs
@@ -142,5 +142,11 @@
   it "doesn't allow more configuration options after a quoted value" $
     parseConfig `shouldFailOn` "foo='bar'baz='buz'"
 
+  it "parses a command $(command)" $ do
+    parseConfig "FOO=$(command)"
+      `shouldParse` [ParsedVariable "FOO" (Unquoted [CommandInterpolation "command"])]
+    parseConfig "FOO=asdf_$(command)"
+      `shouldParse` [ParsedVariable "FOO" (Unquoted [VarLiteral "asdf_", CommandInterpolation "command"])]
+
 parseConfig :: String -> Either (ParseError Char Void) [ParsedVariable]
 parseConfig = parse configParser ""
diff --git a/spec/Configuration/DotenvSpec.hs b/spec/Configuration/DotenvSpec.hs
--- a/spec/Configuration/DotenvSpec.hs
+++ b/spec/Configuration/DotenvSpec.hs
@@ -7,6 +7,7 @@
 
 import Test.Hspec
 
+import System.Process (readCreateProcess, shell)
 import System.Environment (lookupEnv)
 import Control.Monad (liftM)
 import Data.Maybe (fromMaybe)
@@ -111,6 +112,11 @@
     it "recognises previous variables" $
       liftM (!! 3) (parseFile "spec/fixtures/.dotenv") `shouldReturn`
         ("PREVIOUS", "true")
+
+    it "recognises commands" $ do
+      me <- init <$> readCreateProcess (shell "whoami") ""
+      liftM (!! 4) (parseFile "spec/fixtures/.dotenv") `shouldReturn`
+        ("ME", me)
 
   describe "onMissingFile" $ after_ (unsetEnv "DOTENV") $ do
     context "when target file is present" $
diff --git a/spec/fixtures/.dotenv b/spec/fixtures/.dotenv
--- a/spec/fixtures/.dotenv
+++ b/spec/fixtures/.dotenv
@@ -2,3 +2,4 @@
 UNICODE_TEST=Manabí
 ENVIRONMENT="$HOME"
 PREVIOUS="$DOTENV"
+ME="$(whoami)"
diff --git a/src/Configuration/Dotenv/Parse.hs b/src/Configuration/Dotenv/Parse.hs
--- a/src/Configuration/Dotenv/Parse.hs
+++ b/src/Configuration/Dotenv/Parse.hs
@@ -60,14 +60,24 @@
 quotedWith DoubleQuote = DoubleQuoted <$> (between (char '\"') (char '\"') $ many (fragment "\""))
 
 fragment :: [Char] -> Parser VarFragment
-fragment charsToEscape = interpolatedValueFragment <|> literalValueFragment ('$' : '\\' : charsToEscape)
+fragment charsToEscape =
+  interpolatedValueCommandInterpolation
+    <|> interpolatedValueVarInterpolation
+    <|> literalValueFragment ('$' : '\\' : charsToEscape)
 
-interpolatedValueFragment :: Parser VarFragment
-interpolatedValueFragment = VarInterpolation <$>
+interpolatedValueVarInterpolation :: Parser VarFragment
+interpolatedValueVarInterpolation = VarInterpolation <$>
                             ((between (symbol "${") (symbol "}") variableName) <|>
                             (char '$' >> variableName))
   where
     symbol                = L.symbol sc
+
+interpolatedValueCommandInterpolation :: Parser VarFragment
+interpolatedValueCommandInterpolation =
+  CommandInterpolation
+    <$> between (symbol "$(") (symbol ")") (many alphaNumChar)
+    where
+      symbol = L.symbol sc
 
 literalValueFragment :: [Char] -> Parser VarFragment
 literalValueFragment charsToEscape = VarLiteral <$> (some $ escapedChar <|> normalChar)
diff --git a/src/Configuration/Dotenv/ParsedVariable.hs b/src/Configuration/Dotenv/ParsedVariable.hs
--- a/src/Configuration/Dotenv/ParsedVariable.hs
+++ b/src/Configuration/Dotenv/ParsedVariable.hs
@@ -13,6 +13,7 @@
 #endif
 import Control.Applicative ((<|>))
 import System.Environment (lookupEnv)
+import System.Process (readCreateProcess, shell)
 
 data ParsedVariable
   = ParsedVariable VarName VarValue deriving (Show, Eq)
@@ -28,7 +29,8 @@
 
 data VarFragment
   = VarInterpolation String
-  | VarLiteral String deriving (Show, Eq)
+  | VarLiteral String
+  | CommandInterpolation String deriving (Show, Eq)
 
 interpolateParsedVariables :: [ParsedVariable] -> IO [(String, String)]
 interpolateParsedVariables = fmap reverse . foldM addInterpolated []
@@ -49,9 +51,11 @@
 interpolateFragment previous (VarInterpolation varname) = fromPreviousOrEnv >>= maybe (return "") return
   where
     fromPreviousOrEnv = (lookup varname previous <|>) <$> lookupEnv varname
+interpolateFragment _ (CommandInterpolation commandName) = init <$> readCreateProcess (shell commandName) ""
 
 joinContents :: VarContents -> String
 joinContents = concatMap fragmentToString
   where
+    fragmentToString (CommandInterpolation value) = value
     fragmentToString (VarInterpolation value) = value
     fragmentToString (VarLiteral value)       = value