remove and replace text in a .dat file

Hi,

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

Answer 1

[Jan]

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');
fclose(fid);

[Joshua Ford]

Hi thanks for this. It worked really well.

I have a similar instance where I want to change a numerical value within a text file automatically. For instance the structure is:

100 Number

and I want to change it to

10 Number

How would I do this? I want to search for the word Number in the text file and then go back along the line to change the number?

[Jan]

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);