MATLAB: Copy a txt file and change a line by a other

copystringtxt file

Dear I have a problem to copy from a txt file to another one, and change a specific line i have found the copy file option

file_A = 'Ok_A.txt';
file_B = 'Ok_B.txt';
copyfile(file_A,file_B)

But i cannot go further

Best Answer

copyfile() is not appropriate for this. You need to fopen() one file for input and the other for output, and then copy the input to the output until you get to the line that is to be changed. Output the changed version of the line rather than the original version of the line. Then continue copying input to output until the end of file. Then fclose() the two files.

There is no way to make a change in the "middle" of a text file -- not unless the new text is exactly the same size as the original text. This is not a restriction imposed by MATLAB: it is a restriction on all file systems that have been implemented by vendors over the last 30-ish years.

Related Solutions

MATLAB: How to replace a portion of data with another

This works. The example input and output files are attached.

newData = [1,2;3,4;5,6;7,8];
newName = 'blah.prw';
fid = fopen('oldfile.txt', 'rt');
fod = fopen('newfile.txt', 'wt');
for k = 1:3
    fprintf(fod,'%s\n',fgetl(fid));
end
str = regexprep(fgetl(fid),'\w+\.prw',newName);
fprintf(fod,'%s\n',str)
cmp = ' !-';
while ~isequal(intersect(str,cmp),cmp)
    str = fgetl(fid);
    fprintf(fod,'%s\n',str)
end
fprintf(fod,'          %.7f          %.7f\n',newData.')
while ~isempty(str)
    str = strtrim(fgetl(fid))
end
fprintf(fod,'          \n')
while ~feof(fid)
    fprintf(fod,'%s\n',fgetl(fid))
end
fclose(fid);
fclose(fod);

MATLAB: How to convert ‘comma’ to ‘dot’

You can use my function fstrrep to replace each . with a , and then use dlmread to read the data:

fstrrep('test22.txt', ',', '.')
data = dlmread('test22.txt')

The m-file:

function fstrrep(filename, oldsubstr, newsubstr, newfilename)
%FSTRREP Replace string in file.
%


%FSTRREP(FILENAME, OLDSUBSTR, NEWSUBSTR, [NEWFILENAME])read each line in
%FILENAME and replaces the string OLDSUBSTR with NEWSUBSTR and writes the
%new line to NEWFILENAME. If the optional argument NEWFILENAME is not
%given, the contents of the original file is changed.
%
%Example: In file 'test.txt', replace each ',' with a '.'
%  fstrrep('test.txt', ',' '.')
%
%Thorsten.Hansen@psychol.uni-giessen.de
%%open file to read from and new file to write to
fid1 = fopen(filename, 'r');
if fid1 == -1
  error(['Cannot open file ' filename ' for reading.']);
end
if nargin < 4
  newfilename = '_temp.txt';
end
fid2 = fopen(newfilename, 'w');
if fid2 == -1
  error(['Cannot open file ' newfilename ' for writing.']);
end
%%read line and write changed line to new file
line = fgets(fid1);
while line ~= -1
  newline = strrep(line, oldsubstr, newsubstr);
  fprintf(fid2, '%s', newline);
  line = fgets(fid1);
end
%%close both files
st = fclose(fid1);
if st == -1
  error(['Cannot close ' filename '.'])
end
st = fclose(fid2);
if st == -1
  error(['Cannot close ' tempfilename '.'])
end
%%replace old file with new file
if nargin < 4
  movefile(newfilename, filename)
end

Best Answer

Related Solutions

MATLAB: How to replace a portion of data with another

MATLAB: How to convert ‘comma’ to ‘dot’

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