Flag passed to the shell to execute "!" and ":!" commands; e.g., "bash.exe -c ls", "powershell.exe -Command dir", or "cmd.exe /c dir". For MS-Windows, the default is set according to the value of 'shell', to reduce the need to set this option by the user. On Unix it can have more than one flag. Each white space separated part is passed as an argument to the shell command. See |option-backslash| about including spaces and backslashes. Also see |dos-shell| and |dos-powershell| for MS-Windows. This option cannot be set from a |modeline| or in the |sandbox|, for security reasons.