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: ncaddhis_documentation.m
    path of file: ./repos/CDT/cdt/doc
    
    the code of the file until where you have to start completion: %% |ncaddhis| documentation
%
% This function prepends a dated string to a netCDF file's history
% attribute.
%
% NetCDF best practices recommend that all netCDF files contain a history
% attribute that is updated whenever the file contents are modified.  Some
% netCDF software packages perform this task automatically, but Matlab's
% netCDF-writing and modifying utilities do not.  This function simplifies
% the task of adding a new history attribute if one does not yet exist in a
% file, or preprending a new line to it (rather than overwriting existing
% content) if the attribute already exists.
%
% <CDT_Contents.html Back to Climate Data Tools Contents>
%
%% Syntax
%
%  ncaddhis(file, hisstr)
%
%% Description
%
% |ncaddhis(file, hisstr)| prepends the character array or scalar string
% |hisstr| to the global history attribute within the existing netCDF file
% |file|.  The string will be preceded by the date and time at which this
% function is called.
%
%% Example
%
% For this example, we'll start with the ERA_Interim_2017.nc sample dataset
% that comes with CDT.  Like many climate datasets, this file already
% includes a history attribute that gives us some information about where
% the data came from:

ncreadatt('ERA_Interim_2017.nc', '/', 'history')

%% 
% In this case, we can see that the file was created using the
% grib_to_netcdf-2.9.2 software, and was retrieved in December 2018.
%
% Some tools, such as the <http://nco.sourceforge.net netCDF operator
% utilities (NCO)>, automatically add to the history attribute whenever they
% are used.  For example, let's extract a single grid cell (at 0N,0E) of
% data from the ERA file (you will need NCO installed on your system to run this
% command; if not, don't worry about it, because this is 
    
function prepends a dated string to a netCDF file's history
% attribute.
%
% NetCDF best practices recommend that all netCDF files contain a history
% attribute that is updated whenever the file contents are modified.  Some
% netCDF software packages perform this task automatically, but Matlab's
% netCDF-writing and modifying utilities do not.  This function simplifies
% the task of adding a new history attribute if one does not yet exist in a
% file, or preprending a new line to it (rather than overwriting existing
% content) if the attribute already exists.
%
% <CDT_Contents.html Back to Climate Data Tools Contents>
%
%% Syntax
%
%  ncaddhis(file, hisstr)
%
%% Description
%
% |ncaddhis(file, hisstr)| prepends the character array or scalar string
% |hisstr| to the global history attribute within the existing netCDF file
% |file|.  The string will be preceded by the date and time at which this
% function is called.
%
%% Example
%
% For this example, we'll start with the ERA_Interim_2017.nc sample dataset
% that comes with CDT.  Like many climate datasets, this file already
% includes a history attribute that gives us some information about where
% the data came from:

ncreadatt('ERA_Interim_2017.nc', '/', 'history')

%% 
% In this case, we can see that the file was created using the
% grib_to_netcdf-2.9.2 software, and was retrieved in December 2018.
%
% Some tools, such as the <http://nco.sourceforge.net netCDF operator
% utilities (NCO)>, automatically add to the history attribute whenever they
% are used.  For example, let's extract a single grid cell (at 0N,0E) of
% data from the ERA file (you will need NCO installed on your system to run this
% command; if not, don't worry about it, because this is just for
% demonstration purposes).

system('ncks -d latitude,0.0 -d longitude,0.0 ../cdt_data/ERA_Interim_2017.nc ERA_Interim_2017_00.nc');

%%
% The newly-created file includes an updated line in the history attribute
% that reflects the command we just use used to extract it:

ncreadatt('ERA_Interim_2017_00.nc', '/', 'history')

%%
% However, if we make changes using Matlab's utilities, those are not
% automatically documented.

oldtemp = ncread('ERA_Interim_2017_00.nc', 't2m');
newtemp = oldtemp + 1;
ncwrite('ERA_Interim_2017_00.nc', 't2m', newtemp);

%%
% We can use |ncaddhis| to quickly document this change.

ncaddhis('ERA_Interim_2017_00.nc', 'Added 1 degK to all t2m values (ncaddhis_documentation.m script)');
ncreadatt('ERA_Interim_2017_00.nc', '/', 'history')

%%
% There are no strict rules about what information to include in a history
% statement.  The
% <https://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/build/ch02s06.html
% Climate and Forecast (CF) standards> suggest that "Well-behaved generic
% netCDF filters will automatically append