Parse the folder for existing 1-1000.out files and import them one-by-one apply filter and save:
% Retrieve all the files in a directory
names = dir('C:\Users\Oleg\Desktop\Nuova cartella');
names = {names(~[names.isdir]).name};
% Select only the files #.out
idx = ~cellfun('isempty',regexp(names,'\d+\.out'));
names = names(idx);
% Filter
[b,a] = butter(9,.02,'low');
for n = names
% Open file for reading
fid = fopen([myDir n{:}],'r');
x = textscan(fid,'%f');
y = filter(b,a,cat(1,x{:}));
% Discard content and write filtered data
fid = fopen([myDir n{:}],'w');
fprintf(fid,'%E\r\n',y);
fid = fclose(fid);
end
Oleg
