Copy every Nth line algorithm (octave)

NthLineCopy.m

clear all

function newFinal = addAndConcat(oldFinal, newEnding)
  % Copy every 30th line
  N=30;
  fid = newEnding;
  % Delete top 3 lines
  C = textread(fid, '%s', 'Delimiter', '\n', 'HeaderLines',3);

  C = C(1:N:length(C));

  newFinal = [oldFinal; C];
end

function newFinal = firstFileAddAndConcat(file)
  % Copy every 30th line
  N=30;
  fid = file;
  % Delete top 3 lines
  newFinal = textread(fid, '%s', 'Delimiter', '\n', 'HeaderLines',3);

  newFinal = newFinal(1:N:length(newFinal));
end

newFinal = firstFileAddAndConcat('.csv');
newFinal = addAndConcat(newFinal, '.csv'); 
newFinal = addAndConcat(newFinal, '.csv'); 
% etc.

fid = fopen('FINAL_ALL.txt','wt');
formatSpec = '%s\n';
[nrows,ncols] = size(newFinal);
for row = 1:nrows
    fprintf(fid,formatSpec,newFinal{row,:});
end
fclose(fid);