remove and replace text in a .dat file

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Joshua Ford
Joshua Ford on 17 Oct 2022
Commented: Jan on 18 Oct 2022
I am trying to find a certain line within a .dat file and replace its contents and save it back to the orignal place within matlab. I have been able to find the character position of the text i wish to replace but do not know how to overwrite a specific location of a .dat file.
I have used fileread to read the file as characters and then replace it but cannot find a way to then save that as a .dat file. Any method will be good thank you. I essentially want to replace a lince of text which is a filepath name (assume you dont konw the lenght or contents of the filepath) with a stated filepath

Accepted Answer

Jan on 17 Oct 2022
Edited: Jan on 17 Oct 2022
You cannot replace a line in a text file on the disk directly, because the new text might have another number of characters than the old one.
FileName = 'C:\Your\file.dat';
C = fileread(FileName);
C = strrep(C, oldText, newText);
% Modern Matlab versions (since R2022a):
writelines(C, FileName);
% Old Matlab versions:
[fid, msg] = fopen(FileName, 'w');
assert(fid > 0, msg);
fwrite(fid, C, 'char');
Jan on 18 Oct 2022
If your are 100 percent sure, that such a case cannot happen:
100 Number % original line
100000000000 Number % new line
you could overwrite the part without writing the complete file. But if the file is small, this is easier:
FileName = 'C:\Your\file.dat';
C = readlines(FileName);
m = contains(C, 'Number');
C(m) = sprintf("%-10d Number", 100);
writelines(C, FileName);

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