You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: ft_read_sens.m
    path of file: ./repos/spm12/external/fieldtrip/fileio
    
    the code of the file until where you have to start completion: function [sens] = ft_read_sens(filename, varargin)

% FT_READ_SENS read sensor positions from various manufacturer specific files. See
% further down for the list of file types that are supported.
%
% Use as
%   grad = ft_read_sens(filename, ...)  % for gradiometers
%   elec = ft_read_sens(filename, ...)  % for electrodes

    
function [sens] = ft_read_sens(filename, varargin)

% FT_READ_SENS read sensor positions from various manufacturer specific files. See
% further down for the list of file types that are supported.
%
% Use as
%   grad = ft_read_sens(filename, ...)  % for gradiometers
%   elec = ft_read_sens(filename, ...)  % for electrodes
%
% Additional options should be specified in key-value pairs and can be
%   'fileformat'     = string, see the list of supported file formats (the default is determined automatically)
%   'senstype'       = string, can be 'eeg', 'meg' or 'nirs', specifies which type of sensors to read from the file (default = 'eeg')
%   'coordsys'       = string, 'head' or 'dewar' (default = 'head')
%   'coilaccuracy'   = scalar, can be empty or a number (0, 1 or 2) to specify the accuracy (default = [])
%
% The electrode, gradiometer and optode structures are defined in more detail 
% in FT_DATATYPE_SENS.
%
% Files from the following acquisition systems and analysis platforms file formats
% are supported.
%   asa_elc besa_elp besa_pos besa_sfp yokogawa_ave yokogawa_con yokogawa_raw 4d
%   4d_pdf 4d_m4d 4d_xyz ctf_ds ctf_res4 itab_raw itab_mhd netmeg neuromag_fif
%   neuromag_mne neuromag_mne_elec neuromag_mne_grad polhemus_fil polhemus_pos
%   zebris_sfp spmeeg_mat eeglab_set localite_pos artinis_oxy3 artinis_oxyproj matlab
%
% See also FT_READ_HEADER, FT_DATATYPE_SENS, FT_PREPARE_VOL_SENS, FT_COMPUTE_LEADFIELD,

% Copyright (C) 2005-2018 Robert Oostenveld
%
% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org
% for the documentation and details.
%
%    FieldTrip is free software: you can redistribute it and/or modify
%    it under the terms of the GNU General Public License as published by
%    the Free Software Foundation, either version 3 of the License, or
%    (at your option) any later version.
%
%    FieldTrip is distributed in the hope that it will be useful,
%    but WITHOUT ANY WARRANTY; without even the implied warranty of
%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%    GNU General Public License for more details.
%
%    You should have received a copy of the GNU General Public License
%    along with FieldTrip. If not, see <http://www.gnu.org/licenses/>.
%
% $Id$

% optionally get the data from the URL and make a temporary local copy
filename = fetch_url(filename);

% get the options
fileformat     = ft_getopt(varargin, 'fileformat', ft_filetype(filename));
senstype       = ft_getopt(varargin, 'senstype');         % can be eeg or meg, default is automatic when []
coordsys       = ft_getopt(varargin, 'coordsys', 'head'); % this is used for ctf and neuromag_mne, it can be head or dewar
coilaccuracy   = ft_getopt(varargin, 'coilaccuracy');     % empty, or a number between 0 to 2

realtime = any(strcmp(fileformat, {'fcdc_buffer', 'ctf_shm', 'fcdc_mysql'}));

if realtime
  % skip the rest of the initial checks to increase the speed for realtime operation
else
  % test whether the file exists
  if ~exist(filename, 'file')
    ft_error('file ''%s'' does not exist', filename);
  end