diff --git a/cmd/block_test.go b/cmd/block_test.go
new file mode 100644
index 0000000..001509b
--- /dev/null
+++ b/cmd/block_test.go
@@ -0,0 +1,7 @@
+package cmd_test
+
+import "testing"
+
+func TestBlockCommand(t *testing.T) {
+	runScript(t, "testdata/script/block.txtar")
+}
diff --git a/cmd/file.go b/cmd/file.go
index 4cbddca..d0c78d4 100644
--- a/cmd/file.go
+++ b/cmd/file.go
@@ -2,22 +2,24 @@ package cmd
 
 import (
 	"fmt"
-	"io"
 	"os"
 
+	"litdoc/internal"
+
 	"github.com/spf13/cobra"
 )
 
 var fileCmd = &cobra.Command{
-	Use:   "file",
+	Use:   "file <path>",
 	Short: "Process a file",
+	Args:  cobra.ExactArgs(1),
 	Run: func(cmd *cobra.Command, args []string) {
-		data, err := io.ReadAll(os.Stdin)
+		data, err := internal.ProcessFile(args[0])
 		if err != nil {
 			fmt.Fprintln(os.Stderr, err)
 			os.Exit(1)
 		}
-		fmt.Print(string(data))
+		fmt.Print(data)
 	},
 }
 
diff --git a/cmd/file_test.go b/cmd/file_test.go
new file mode 100644
index 0000000..62200d7
--- /dev/null
+++ b/cmd/file_test.go
@@ -0,0 +1,34 @@
+package cmd_test
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"litdoc/cmd"
+
+	"github.com/rogpeppe/go-internal/testscript"
+)
+
+func TestMain(m *testing.M) {
+	testscript.Main(m, map[string]func(){
+		"litdoc": func() {
+			if err := cmd.Execute(); err != nil {
+				fmt.Fprintln(os.Stderr, err)
+				os.Exit(1)
+			}
+		},
+	})
+}
+
+func TestFileCommand(t *testing.T) {
+	runScript(t, "testdata/script/file.txtar")
+}
+
+func runScript(t *testing.T, script string) {
+	t.Helper()
+
+	testscript.Run(t, testscript.Params{
+		Files: []string{script},
+	})
+}
diff --git a/testdata/script/block.txtar b/cmd/testdata/script/block.txtar
similarity index 100%
rename from testdata/script/block.txtar
rename to cmd/testdata/script/block.txtar
diff --git a/testdata/script/file.txtar b/cmd/testdata/script/file.txtar
similarity index 56%
rename from testdata/script/file.txtar
rename to cmd/testdata/script/file.txtar
index 5809cf5..d8aafae 100644
--- a/testdata/script/file.txtar
+++ b/cmd/testdata/script/file.txtar
@@ -1,5 +1,4 @@
-stdin input.md
-exec litdoc file
+exec litdoc file input.md
 stdout '# Hello'
 
 -- input.md --
diff --git a/main_test.go b/main_test.go
deleted file mode 100644
index 36bbea9..0000000
--- a/main_test.go
+++ /dev/null
@@ -1,23 +0,0 @@
-package main_test
-
-import (
-	"os"
-	"path/filepath"
-	"testing"
-
-	"github.com/rogpeppe/go-internal/testscript"
-)
-
-func TestScript(t *testing.T) {
-	binPath, err := filepath.Abs("bin")
-	if err != nil {
-		t.Fatal(err)
-	}
-	testscript.Run(t, testscript.Params{
-		Dir: "testdata/script",
-		Setup: func(env *testscript.Env) error {
-			env.Setenv("PATH", binPath+string(os.PathListSeparator)+env.Getenv("PATH"))
-			return nil
-		},
-	})
-}