How can i replace a line form a text ?

I have the following text file i want to replace all the line that contains this pattern X = 259.557 mm, Y = 563.173 mm, Z = -104.284 mm,

with a new line that contains the existing numbers added by a certain value.

Answer 1

[Stephen23]

You can easily match those lines using a regular expression. Something like this:

fmt = sprintf('\\s*%c\\s*=\\s*(\\d+\\.\\d+)\\s*mm,','XYZ')
fmt = sprintf('^%s\\s*$',fmt)
str = fileread('values.txt');
spl = regexp(str,'[\n\r]+','split');
tmp = regexp(spl,fmt,'tokens','once');
idx = find(~cellfun('isempty',tmp));
for k = reshape(idx,1,[])
    vec = str2double(tmp{k}) + 2; % add two as example data manipulation.
    spl{k}  = sprintf(' X = %.3f, Y = %.3f, Z = %.3f,',vec);
end
fid = fopen('newfile.txt','wt');
fprintf(fid,'%s\n',spl{:});
fclose(fid);

[Theodor Al Saify]

nothing has changed when i run the code , Do i need to modify anything in it ?

[Stephen23]

It creates a new file called 'newfile.txt' Check that file and you will see that each X,Y,Z value has increased by two, as the comment describes.

You could overwrite the original file, but I would not recommend doing this until the code has been well tested.

[Theodor Al Saify]

I found that the problem is for the (-) sign sometimes the numbers are negative and won't match the pattern. Do you know how i can fix it ?

[Stephen23]

Change the first line to this:

fmt = sprintf('\\s*%c\\s*=\\s*([-+]?\\d+\\.\\d+)\\s*mm,','XYZ')
                               ^^^^^ optional +/- sign

[Theodor Al Saify]

Thank you it work perfectly . :D