diff --git a/app/Main.hs b/app/Main.hs
index e64235e..850abe7 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -34,7 +34,10 @@ options =
           <> short 'i'
           <> help "read input from stdin, pipe into program continually"
       )
-    <*> some (argument str (metavar "COMMAND ARGS"))
+    <*> argument str
+      ( metavar "COMMAND"
+          <> action "command" )
+    <*> some (argument str (metavar "[ARGS]"))
 
 main :: IO ()
 main = do
diff --git a/flake.nix b/flake.nix
index 27730f1..72d09f1 100644
--- a/flake.nix
+++ b/flake.nix
@@ -30,6 +30,7 @@
             };
           nativeBuildInputs = with pkgs; [
             git
+            installShellFiles
             python3
           ];
           devTools = let inherit (pkgs) bazel-watcher buildifier haskell-language-server lib; in
@@ -73,6 +74,11 @@
               '';
               installPhase = ''
                 install -D -t $out/bin bazel-bin/replay
+
+                installShellCompletion --cmd replay \
+                   --bash <( bazel-bin/replay --bash-completion-script $out/bin/replay ) \
+                   --fish <( bazel-bin/replay --fish-completion-script $out/bin/replay ) \
+                   --zsh <( bazel-bin/replay --zsh-completion-script $out/bin/replay )
               '';
             };
           };
diff --git a/src/Lib.hs b/src/Lib.hs
index 8552d56..e819c3b 100644
--- a/src/Lib.hs
+++ b/src/Lib.hs
@@ -20,6 +20,7 @@ data Options = Options
   { varName    :: String,
     watchFiles :: [String],
     useStdin   :: Bool,
-    cmdline    :: [String]
+    command    :: String,
+    args       :: [String]
   }
   deriving (Show)
diff --git a/src/UI.hs b/src/UI.hs
index 78316ba..6fda2a0 100644
--- a/src/UI.hs
+++ b/src/UI.hs
@@ -111,7 +111,8 @@ rerun =
   do
     state <- gets formState
     let text = state ^. input
-        cmdargs = cmdline $ options state
+        opt = options state
+        cmdargs = command opt : args opt
     out <- liftIO do
       let stdin = state ^. stdInput
       runExceptT $ getOutput cmdargs (DT.unpack text) stdin