From 2568dc45c2e4fb40e99f1290a4560b7ec429b239 Mon Sep 17 00:00:00 2001
From: Leon Mika <lmika@lmika.org>
Date: Tue, 8 Sep 2026 20:47:47 +1000
Subject: [PATCH] Fixed arg order of os bang

---
 ucl/builtins/os.go      | 23 ++++++++++++++---------
 ucl/builtins/os_test.go |  7 +++++--
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/ucl/builtins/os.go b/ucl/builtins/os.go
index 925f9c8..0f3da1d 100644
--- a/ucl/builtins/os.go
+++ b/ucl/builtins/os.go
@@ -93,11 +93,20 @@ func (oh osHandlers) exec(ctx context.Context, args ucl.CallArgs) (any, error) {
 
 func (oh osHandlers) bang(ctx context.Context, args ucl.CallArgs) (any, error) {
 	var (
-		cmdStr string
+		cmdStr   string
+		stdIn    string
+		hasStdin bool
 	)
 
-	if err := args.Bind(&cmdStr); err != nil {
-		return nil, err
+	if args.NArgs() == 1 {
+		if err := args.Bind(&cmdStr); err != nil {
+			return nil, err
+		}
+	} else {
+		if err := args.Bind(&stdIn, &cmdStr); err != nil {
+			return nil, err
+		}
+		hasStdin = true
 	}
 
 	cmd, err := oh.provider.ExecBang(ctx, cmdStr)
@@ -105,12 +114,8 @@ func (oh osHandlers) bang(ctx context.Context, args ucl.CallArgs) (any, error) {
 		return nil, err
 	}
 
-	if args.NArgs() > 0 {
-		var stdin string
-		if err := args.Bind(&stdin); err != nil {
-			return nil, err
-		}
-		cmd.Stdin = strings.NewReader(stdin)
+	if hasStdin {
+		cmd.Stdin = strings.NewReader(stdIn)
 	}
 
 	res, err := cmd.Output()
diff --git a/ucl/builtins/os_test.go b/ucl/builtins/os_test.go
index 748d632..ed30ba5 100644
--- a/ucl/builtins/os_test.go
+++ b/ucl/builtins/os_test.go
@@ -69,8 +69,11 @@ func TestOS_Bang(t *testing.T) {
 	}{
 		{descr: "run command 1", eval: `os:! "echo 'hello, world'"`, want: "hello, world\n"},
 		{descr: "run command 2", eval: `os:! "date +%Y%m%d"`, want: time.Now().Format("20060102") + "\n"},
-		{descr: "run command 3", eval: `os:! "tr [a-z] [A-Z]" "hello"`, want: "HELLO"},
-		{descr: "run command 4", eval: `os:! "tr -d e" "hello"`, want: "hllo"},
+		{descr: "run command 3", eval: `os:! "hello" "tr [a-z] [A-Z]"`, want: "HELLO"},
+		{descr: "run command 4", eval: `os:! "hello" "tr -d e" "hello"`, want: "hllo"},
+		{descr: "run command 5", eval: `"hello" | os:! "tr [a-z] [A-Z]"`, want: "HELLO"},
+		{descr: "run command 6", eval: `"hello" | os:! "tr -d e"`, want: "hllo"},
+		{descr: "run command 7", eval: `"hello" | os:! "tr -d e" | os:! "tr [a-z] [A-Z]"`, want: "HLLO"},
 	}
 
 	for _, tt := range tests {