问exec重定向stdin后的Shell注销

EN

   exec [-cl] [-a name] [command [arguments]]
          If command is specified, it replaces the shell.  No new  process
          is  created.  The arguments become the arguments to command.  If
          the -l option is supplied, the shell places a dash at the begin-
          ning  of  the  zeroth  argument passed to command.  This is what
          login(1) does.  The -c option causes command to be executed with
          an  empty environment.  If -a is supplied, the shell passes name
          as the zeroth argument to the executed command.  If command can-
          not  be executed for some reason, a non-interactive shell exits,
          unless the shell option execfail is enabled, in  which  case  it
          returns  failure.   An  interactive shell returns failure if the
          file cannot be executed.  If command is not specified, any redi-
          rections take effect in the current shell, and the return status
          is 0.  If there is a redirection error, the return status is  1.