Validate input and handle errors in RunBangCommand

Add input validation to reject empty commands and properly handle
the error from exec.CommandContext instead of silently discarding it.
When the command fails and produces no output, the error message is
shown to the user.

Fixes #1716

Assisted-By: cagent

Author: dgageot

pkg/app/app.go

@@ -446,8 +446,18 @@ func (a *App) RunWithMessage(ctx context.Context, cancel context.CancelFunc, msg
 }
 
 func (a *App) RunBangCommand(ctx context.Context, command string) {
-	out, _ := exec.CommandContext(ctx, "/bin/sh", "-c", command).CombinedOutput()
-	a.events <- runtime.ShellOutput("$ " + command + "\n" + string(out))
+	command = strings.TrimSpace(command)
+	if command == "" {
+		a.events <- runtime.ShellOutput("Error: empty command")
+		return
+	}
+
+	out, err := exec.CommandContext(ctx, "/bin/sh", "-c", command).CombinedOutput()
+	output := "$ " + command + "\n" + string(out)
+	if err != nil && len(out) == 0 {
+		output = "$ " + command + "\nError: " + err.Error()
+	}
+	a.events <- runtime.ShellOutput(output)
 }
 
 func (a *App) Subscribe(ctx context.Context, program *tea.Program) {