diff --git a/cmdlang/ast.go b/cmdlang/ast.go
index 0943a95..5fe41be 100644
--- a/cmdlang/ast.go
+++ b/cmdlang/ast.go
@@ -12,7 +12,7 @@ type astLiteral struct {
 
 type astCmdArg struct {
 	Literal *astLiteral  `parser:"@@"`
-	Sub     *astPipeline `parser:"| '[' @@ ']'"`
+	Sub     *astPipeline `parser:"| '(' @@ ')'"`
 }
 
 type astCmd struct {