exec [ -cl ] [ -a argv0 ] [ command [ arg ... ] ]
       Replace the current shell with command rather than forking.  If com-
       mand  is a shell builtin command or a shell function, the shell exe-
       cutes it, and exits when the command is complete.

       With -c clear the environment; with -l  prepend  -  to  the  argv[0]
       string  of the command executed (to simulate a login shell); with -a
       argv0 set the argv[0] string of the command executed.  See the  sec-
       tion `Precommand Modifiers' in zshmisc(1).

       If the option POSIX_BUILTINS is set, command is never interpreted as
       a  shell builtin command or shell function.  This means further pre-
       command modifiers such as builtin and noglob  are  also  not  inter-
       preted within the shell.  Hence command is always found by searching
       the command path.

       If  command  is omitted but any redirections are specified, then the
       redirections will take effect in the current shell.
