open( my $fh, "<", $array_ip_list )
  or send_mail("ip_list_error"),
    die "IP List File - nas_array_ip_list.txt not found";

# [ . . . Do lots of stuff here . . . ]

# If our external commands completed successfully, send our e-mail
if ($result_from_nas_check_function) {
    send_mail( "results", $filename );

    # [ Clean up after ourselves, delete our temp file, etc. ]
    exit 0;
}
else {

    # [ Notify e-mail that an error occured ]

    # [ Clean up after ourselves, delete our temp file, etc. ]
    die "Something went wrong.";
}