diff --git a/bin/snack b/bin/snack
new file mode 100755
index 0000000..295163d
--- /dev/null
+++ b/bin/snack
@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+## Defaults
+
+NIX_BUILD=nix-build
+SNACK_NIX=snack.nix
+COMMAND=
+
+## Functions
+
+log_error() {
+  echo "ERROR: $*" >&2
+}
+
+show_usage() {
+  cat <<USAGE
+Usage: snack [options] <command>
+
+Snack is a Haskell build tool
+
+Options:
+  -f | --snack-nix <PATH>: sets the path ot the "snack.nix" file. Default: "./snack.nix"
+  -h | --help: Shows this help
+
+Commands:
+  run: builds and executes
+  build: builds
+  ghci: builds and loads in ghci
+USAGE
+}
+
+## Main
+
+while [[ $# -gt 0 ]]; do
+  key="$1"
+
+  case $key in
+    -f | --snack-nix)
+      SNACK_NIX="$2"
+      shift
+      shift
+      ;;
+    -h | --help)
+      show_usage
+      exit 0
+      ;;
+    run | build | ghci)
+      COMMAND="$1"
+      shift # past argument
+      ;;
+    *) # unknown option
+      echo "unknown option: $1"
+      exit 1
+      ;;
+  esac
+done
+
+if [[ -z "$COMMAND" ]]; then
+  log_error "missing <command>\n"
+  show_usage
+  exit 1
+fi
+
+echo "snack nix: $SNACK_NIX"
+echo "command: $COMMAND"
+
+case $COMMAND in
+  build)
+    "$NIX_BUILD" --no-out-link -A build "$SNACK_NIX"
+    ;;
+  ghci)
+    res=$("$NIX_BUILD" --no-out-link -A ghci "$SNACK_NIX")
+    "$res/bin/ghci"
+    ;;
+  run)
+    res=$("$NIX_BUILD" --no-out-link -A build "$SNACK_NIX")
+    echo "running $res"
+    "$res/out"
+    ;;
+esac
diff --git a/default.nix b/default.nix
index 09d3868..11c7f08 100644
--- a/default.nix
+++ b/default.nix
@@ -1,49 +1,11 @@
 { pkgs ? import ./nix {} }:
 
 { snack-lib = import ./snack/default.nix { inherit pkgs; };
-  snack-exe = pkgs.writeScriptBin "snack"
-      ''
-        set -euo pipefail
-
-        SNACK_NIX=snack.nix
-
-        while [[ $# -gt 0 ]]
-        do
-        key="$1"
-
-        case $key in
-            -f|--snack-nix)
-            SNACK_NIX="$2"
-            shift
-            shift
-            ;;
-            run|build|ghci)
-            COMMAND="$1"
-            shift # past argument
-            ;;
-            *)    # unknown option
-            echo "unknown option: $1"
-            exit 1
-            ;;
-        esac
-        done
-        echo "snack nix: $SNACK_NIX"
-        echo "command: $COMMAND"
-
-        case $COMMAND in
-          build)
-            ${pkgs.nix}/bin/nix-build --no-out-link -A build $SNACK_NIX
-            ;;
-          ghci)
-            res=$(${pkgs.nix}/bin/nix-build --no-out-link -A ghci $SNACK_NIX)
-            $res/bin/ghci
-            ;;
-          run)
-            res=$(${pkgs.nix}/bin/nix-build --no-out-link -A build $SNACK_NIX)
-            echo "running $res"
-            $res/out
-            ;;
-        esac
-      '';
+  snack-exe = pkgs.writeScriptBin
+    "snack"
+    (builtins.replaceStrings
+      ["NIX_BUILD=nix-build"]
+      ["NIX_BUILD=${pkgs.nix}/bin/nix-build"]
+      (builtins.readFile ./bin/snack));
 }
 
diff --git a/script/snack-fmt b/script/snack-fmt
new file mode 100755
index 0000000..4a024cc
--- /dev/null
+++ b/script/snack-fmt
@@ -0,0 +1,4 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -p shfmt -i bash
+cd "$(dirname "$0")/.."
+shfmt -i 2 -w bin/snack
diff --git a/script/test b/script/test
index 61ba479..c7ef6ed 100755
--- a/script/test
+++ b/script/test
@@ -2,23 +2,50 @@
 #!nix-shell -i bash
 #!nix-shell -I nixpkgs=./nix
 #!nix-shell -p snack.snack-exe
+#!nix-shell -p shfmt
 #!nix-shell --pure
 # vim: ft=sh sw=2 et
 
-set -eux
+set -euo pipefail
 
+## Functions
+
+banner() {
+    echo "--- $*"
+}
+
+fail() {
+  echo "ERROR: $*"
+  exit 1
+}
+
+## Main
+
+cd "$(dirname "$0")/.."
+
+banner "Test packages"
 pushd tests/packages
 snack build
 popd
 
+banner "Test Template Haskell"
 pushd tests/template-haskell
 snack build
 popd
 
+banner "Test Template Haskell 2"
 pushd tests/template-haskell-2
 snack build -f code/snack.nix
 popd
 
+banner "Test Template Haskell 3"
 pushd tests/template-haskell-3
 snack build
 popd
+
+banner "Test stack-exe formatting"
+list=$(shfmt -i 2 -l bin/snack)
+if [[ -n "$list" ]]; then
+  fail "Please apply script/snack-fmt to format bin/snack"
+fi
+echo OK