Replace specific line in a text file

Hi everyone,

I have a text file (for example: data.dat) as shown below, with a number of lines.

data.dat

@motion parameters
speed= 22,30,60
range= 600
rotation= 50

@controls
act= 2,3,4,5

I want to read it and replace the line that comes right after the line starting with a specfic keyword e.g. "@controls" . In this case, the line to be replaced is this one

act= 2,3,4,5

and it should be changed in a loop. For an instant, for example, it would change to:

act= 1,0,8,-2

I'd appreciate your help. Thanks in advance.

Answer 1

[Shubham Gupta]

One of the way could be:

fid = fopen('data.dat','r');        % Open File to read
replaceline = 'act= 1,0,8,-2';      % Line to replace

i = 1;
tline = 's';
A = {[]};

while ischar(tline)
    tline = fgetl(fid);
    if ~isempty(strfind(tline,'@controls')) % find '@controls'
        A{i}=tline;
        A{i+1} = replaceline;               % replace line
        tline = fgetl(fid);
        i = i+1;
    else
        A{i}=tline;
    end
    i = i+1;
end
fclose(fid);


fid2=fopen('data.dat','w');            % Open file to write
for i=1:length(A)-1
    fprintf(fid2,['%s',char([13,10])],A{i});
end
fclose(fid2);

Let me know if you have doubts !

[Islam Elnady]

Thank you for help. It worked perfect. But when I changed

A{i+1} = replaceline;

to

A{i} = replaceline;

So that I could replace the same line. If there is a line below the repleaced one, it'll be deleted and replaced with a blank line. What edits should be made to fix this?

[Islam Elnady]

while ischar(tline)
    tline = fgetl(fid);
    if ~isempty(strfind(tline,'@controls'))  % find '@controls'
        A{i}=tline;
        A{i} = replaceline;               % replace line
      %  tline = fgetl(fid);
      %  i = i+1;
    else
        A{i}=tline;
    end
    i = i+1;
end

I figured it out. This will replace the same line that contains the pattern. Thank you again!