Name of the shell to use for ! and :! commands. When changing the value also check these options: 'shelltype', 'shellpipe', 'shellslash' 'shellredir', 'shellquote', 'shellxquote' and 'shellcmdflag'. It is allowed to give an argument to the command, e.g. "csh -f". See |option-backslash| about including spaces and backslashes. Environment variables are expanded |:set_env|.