From e1b53f8bea4b2d614fd65c99ff6f0720b7d08b63 Mon Sep 17 00:00:00 2001
From: Leon Mika <lmika@lmika.org>
Date: Tue, 8 Sep 2026 20:36:39 +1000
Subject: [PATCH] Added os bang

---
 ucl/builtins/os.go      | 36 ++++++++++++++++++++++++++++++++++++
 ucl/builtins/os_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/ucl/builtins/os.go b/ucl/builtins/os.go
index e19c19f..925f9c8 100644
--- a/ucl/builtins/os.go
+++ b/ucl/builtins/os.go
@@ -13,6 +13,7 @@ import (
 type OSProvider interface {
 	LookupEnv(string) (string, bool)
 	Exec(ctx context.Context, cmd string, args ...string) (*exec.Cmd, error)
+	ExecBang(ctx context.Context, cmd string) (*exec.Cmd, error)
 }
 
 type osHandlers struct {
@@ -29,6 +30,7 @@ func OS() ucl.Module {
 		Builtins: map[string]ucl.BuiltinHandler{
 			"env":  osh.env,
 			"exec": osh.exec,
+			"!":    osh.bang,
 		},
 	}
 }
@@ -89,8 +91,42 @@ func (oh osHandlers) exec(ctx context.Context, args ucl.CallArgs) (any, error) {
 	return string(res), nil
 }
 
+func (oh osHandlers) bang(ctx context.Context, args ucl.CallArgs) (any, error) {
+	var (
+		cmdStr string
+	)
+
+	if err := args.Bind(&cmdStr); err != nil {
+		return nil, err
+	}
+
+	cmd, err := oh.provider.ExecBang(ctx, cmdStr)
+	if err != nil {
+		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)
+	}
+
+	res, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+
+	return string(res), nil
+}
+
 type builtinOSProvider struct{}
 
+func (p builtinOSProvider) ExecBang(ctx context.Context, cmd string) (*exec.Cmd, error) {
+	return exec.CommandContext(ctx, "bash", "-c", cmd), nil
+}
+
 func (builtinOSProvider) LookupEnv(key string) (string, bool) {
 	return os.LookupEnv(key)
 }
diff --git a/ucl/builtins/os_test.go b/ucl/builtins/os_test.go
index 78cee7f..748d632 100644
--- a/ucl/builtins/os_test.go
+++ b/ucl/builtins/os_test.go
@@ -60,3 +60,27 @@ func TestOS_Exec(t *testing.T) {
 		})
 	}
 }
+
+func TestOS_Bang(t *testing.T) {
+	tests := []struct {
+		descr string
+		eval  string
+		want  any
+	}{
+		{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"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.descr, func(t *testing.T) {
+			inst := ucl.New(
+				ucl.WithModule(builtins.OS()),
+			)
+			res, err := inst.EvalString(context.Background(), tt.eval)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, res)
+		})
+	}
+}