exec [ -cl ] [ -a argv0 ] [ command [ arg ... ] ]
       Replace the current shell with command  rather  than  forking.   If
       command  is  a shell builtin command or a shell function, the shell
       executes 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
       precommand modifiers such as builtin and noglob are also not inter-
       preted  within the shell.  Hence command is always found by search-
       ing the command path.

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