MATLAB: How to change a specific part in a specific line in a text file

text file

Hi,

I have a txt file and I need to change specific numbers in specific lines,

line 131, a = 10

line 132, b = 30

is any way to change the above lines to:

a = 5

b = 60

Best Answer

contents = fileread('test.txt');
newa = 10;
newb = 123;
newcontents = regexprep(contents, {'^a\S*=\S*\d+', '^b\S*=\S*\d+'}, {sprintf('a = %d', newa), sprintf('b = %d', newb)});
fid = fopen('test_new.txt', 'wt');
fwrite(fid, newcontents);
fclose(fid);

Related Solutions

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

MATLAB: Copy a line from a txt to other txt

Hi!

count = 1;
tline = fgetl(fid01);
while ischar(tline)
count = count + 1;
disp(tline)
if count == 3
fprintf(fid02,'%s\r\n',tline);
end
tline = fgetl(fid01);
end 
fclose(fid01);
fclose(fid02);

You can do as well

for n = 1:3
tline = fgetl(fid01);
end
fprintf(fid02,'%s\r\n',tline);
fclose(fid01);
fclose(fid02);

Best Answer

Related Solutions

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

MATLAB: Copy a line from a txt to other txt

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