How can I change multiple lines in a text file?

I have pasted a portion of a text file which I would like to edit, an example of what the modified file should look like and also my current output. For each material in the a text file I need to change a value, 2.5e8, to a random variable and I would like to generate many verions of the file with different random variables. The code I am using is as below.

clear all
clc
for n=1:1:20
    fin = fopen('Ap1_Tr_Disp_Int.inp')    
    fout = fopen([num2str(n), '.inp'], 'w')
    while ~feof(fin)                                                        
        s = fgetl(fin)                                                     
        r = 2.5e8 + 2.5e7*randn(1,1)
        s = strrep(s, ' 2.5e8, 0', [' ', num2str(r), ', 0'])
        s = strrep(s, ' 2.5e8, 0.005', [' ', num2str(r), ', 0.005'])        
        fprintf(fout,'%s\n',s)                                             
        end
end
fclose(fin)
fclose(fout)

The problem with the code is that it changes both instances of 2.5e8 (see below) to different random variables. I have spent ages trying to figure this out, however I am new to Matlab. Any help would be greatly appreciated!

Original Text File

    *Material, name=Steel_1
    *Elastic
     2e+11, 0.3
    *Plastic
     2.5e8, 0        (I want to change 2.5e8 to a random variable)
     2.5e8, 0.005    (for each material, new variables should be the same)
     1e3, 0.0050001  
    **
    *Material, name=Steel_2
    *Elastic
     2e+11, 0.3
    *Plastic
     2.5e8, 0
     2.5e8, 0.005
     1e3, 0.0050001  
   .....etc

Example of desired output

*Material, name=Steel_1
    *Elastic
     2e+11, 0.3
    *Plastic
     2.7e8, 0
     2.7e8, 0.005
     1e3, 0.0050001  
    **
    *Material, name=Steel_2
    *Elastic
     2e+11, 0.3
    *Plastic
     2.35e8, 0
     2.35e8, 0.005
     1e3 , 0.0050001  
   .....etc

Example of my current output

*Material, name=Steel_1
    *Elastic
     2e+11, 0.3
    *Plastic
     2.3e8, 0
     2.9e8, 0.005         (2.3e8 and 2.9e8 should be the same)
     1e3, 0.0050001  
    **
    *Material, name=Steel_2
    *Elastic
     2e+11, 0.3
    *Plastic
     2.7e8, 0
     2.4e8, 0.005         (2.7e8 and 2.4e8 should be the same)
     1e3 , 0.0050001  
   .....etc

Answer 1

[Nishitha Ayyalapu]

Here is the working code. Small tweaks to your existing code solved the problem.

1.) Generate a random only for new type of material.

2.) Do the String replace only once whenever the line has target string "2.5e08".

doc strfind

Below is the Modified Code:

clear all
clc
for n=1:1:20
    fin   = fopen('Ap1_Tr_Disp_Int.inp') ;   
    fout  = fopen([num2str(n), '.inp'], 'w');
    occur = 1; %counting ooccurrences of the string '2.5e8'

      while ~feof(fin)    
         %generates new random number only for odd num of occurrences   
          if (mod(occur,2))     
           r =  2.5e8 + 2.5e7*randn(1,1);
          end

         s  = fgets(fin);                                                     

          if (~isempty(strfind(s,' 2.5e8'))) 
              reps = num2str(r(1));
              s = strrep(s, ' 2.5e8', [' ',reps])
              occur = occur + 1; %if the target string occurs increment

          end

          fprintf(fout,'%s',s)                                             
       end
  end
  fclose(fin);
  fclose(fout);

Hope this helps !!

[Colin]

Brilliant. Thanks a lot!

Answer 2

[Cedric]

Just for fun, here is a one-liner for reading/replacing (that I write on 3 lines for sake of clarity):

 repl = regexprep( fileread( 'Ap1_Tr_Disp_Int.inp' ), ...
    '(Plastic\s+)2.5e8(.+?)2.5e8', ...                    
    '${sprintf([$1,''%.1e'',$2,''%.1e''],2.5e8+2.5e7*repmat(randn(1),1,2))}' ) ;

As you are always dealing with the same source file, the whole code would reduce to something like ..

 content = fileread( 'Ap1_Tr_Disp_Int.inp' ) ;
 newContent = @() regexprep( content, ...
    '(Plastic\s+)2.5e8(.+?)2.5e8', ...                    
    '${sprintf([$1,''%.1e'',$2,''%.1e''],2.5e8+2.5e7*repmat(randn(1),1,2))}' ) ;

 for k = 1 : 20
    fid = fopen( sprintf('%02d.inp', k), 'w' ) ;
    fwrite( fid, newContent() ) ;
    fclose( fid ) ;
 end

[Colin]

Thanks for the suggestion. It appears to be much more efficient that any other solutions I have tried.

[Cedric]

You're welcome. The drawback is that it involves a call to REGEXPPREP that nobody will ever want to debug if there is a problem ;-)