Delete lines from text file

How can I delete all the lines form a text file after the line number x and store it in another test file?

Answer 1

[Image Analyst]

As shown in the help:

fid = fopen('fgetl.m');

tline = fgetl(fid);
while ischar(tline)
    disp(tline)
    tline = fgetl(fid);
end

fclose(fid);

Now just modify that to open 2 files, and add a line counter then break after you've transferred x of them (untested)

fin = fopen('input.txt');
fout = fopen('output.txt', 'wt');

tline = fgetl(fin);
count = 0;
while ischar(tline) && count < x
    disp(tline)
    tline = fgetl(fin);
    if ischar(tline)
        fprintf(fout, '%s\n', tline);
    end
    count = count + 1;
end
fclose(fin);
fclose(fout);

[Sergio]

this worked perfect! Thank you!

[Josh Murman]

Add ~strcmp(tline,'Expected Line Text to Remove') to the if statement if you would like to remove a line with that string. Also move the fgetl function in the while loop so the first line isn't skipped.

fin = fopen('input.txt');
fout = fopen('output.txt', 'wt');
tline = fgetl(fin);
while ischar(tline)
    if ~strcmp(tline,'Expected Line Text to Remove') && ischar(tline)
        fprintf(fout, '%s\n', tline);
    end
    tline = fgetl(fin);
    count = count + 1;
end
fclose(fin);
fclose(fout);

Answer 2

[dpb]

Read line 1:x from 1 and copy to the second. Close the second. Done.

Alternatively, rather than line-by-line, read the whole file if it's small enough to fit in memory relatively easily and if x is a sizable fraction of the total number of lines. Then just save data(1:x,:) to the new file.

That's the thing about sequential files---they're, well, 'sequential'.