Replace string in text file

I have a txt file in which there are a bunch of lines. The first two lines are shown below:

10125731872 50  3731  -9999    307    166  -9999    827   4090  -9999    587    332      5  -9999
10125731873 50   117    322      9  -9999    187    300   1273    280    103  -9999     39  -9999

I need to add an "M" after all -9999 values. In a text editor this would be simply done by using the replace tool while looking for all "-9999 " and replacing them with "-9999M". Simple! But I have a hard time doing the same thing in Matlab.

Any idea how I can do this simple task?

Thanks.

Answer 1

[Walter Roberson]

filename = 'a_txt_file.txt';
new_filename = ['new_' filename];

S = fileread(filename);
S = regexprep(S, '-9999\>', '$&M');

fid = fopen(new_filename, 'w');
fwrite(fid, S);
fclose(fid);

It is recommended that new_filename be different than filename: otherwise if something goes wrong in the writing process, you could lose your only copy of the input.

[Kian]

Thanks for the quick answer.

It works, but there is still a small problem. See this is what I got using the syntax you gave me:

10125731872 50  3731  -9999M    307    166  -9999M    827   4090  -9999M    587    332      5  -9999M
10125731873 50   117    322      9  -9999M    187    300   1273    280    103  -9999M     39  -9999M

while this is what I am looking for:

10125731872 50  3731  -9999M   307    166  -9999M   827   4090  -9999M   587    332      5  -9999M
10125731873 50   117    322      9  -9999M   187    300   1273    280    103  -9999M    39  -9999M

Basically, the space that goes after -9999 should be replace with M (rather than just adding an M after -9999 (to keep the formatting of the original txt).

Thanks again.

[Kian]

Okay, I think I found a quick way:

S = regexprep(S, '-9999 \>', '-9999M');

But thanks anyway. It was easy peasy (with the hint you gave me of course)!

[Kian]

Just another point here. The syntax I suggested:

S = regexprep(S, '-9999 \>', '-9999M');

replaces only those -9999 which are in the middle of each line (as they have a space after), but those -9999 at the end of the lines were left out (as they don't have any space after). So once I ran the above regexprep, I had to repeat another one as follows to add M after those -9999 that are the end of each line:

S = regexprep(S, '-9999\>', '-9999M');

Kind of not very neat, but at least it worked. Thanks again for the assistance.

[Walter Roberson]

regexprep(S, '-9999( |$)', '-9999M', 'lineanchors' )

[Kian]

Thanks a lot. This is really neat!

Answer 2

[kuchina mani chandra]

Function replaceStringIntxtFile(filepath,stringToReplace,ReplaceWith) Filedata = readlines(filepath); replacedFiledata =replace(Filedata,stringToReplace,ReplaceWith); F=fopen(filepath,'w'); fprintf(f,'%s\n'replacedFiledata); fclose(f) end