Extracting data from text file only between certain words

I have a really big text file with a ton of data. I only want some of the information. In this case, it's grid properties, which is irrelevant to the question. I want to disregard everything in the text file except the data between the words "BOUNDARY GRID DATA" and "SPOINT DATA." It looks like this essentially:

BOUNDARY GRID DATA

GRID*            5250001         5200000 0.730198500E+02-0.177000000E+03
*       -0.512716000E+02         5200000               0               0
GRID*            5250002         5200000 0.730198500E+02-0.176250000E+03
*       -0.512716000E+02         5200000               0               0
GRID*            5250003         5200000 0.730198500E+02-0.175500000E+03
*       -0.512716000E+02         5200000               0               0
GRID*            5250004         5200000 0.730198500E+02-0.174750000E+03
*       -0.512716000E+02         5200000               0               0

%so on for many more grids


SPOINT DATA 

So I'm struggling to figure out a good way to open this text file and only extract this data. The data for each grid is also in two rows, so I also have to worry about that, but I think I can work through that. The data extraction is the biggest problem. Thanks in advance!

Edit: This is what I have so far

filename = 'Fairing2_FS.asm';


fid1 = fopen(filename);
fid2 = fopen('grid_points.txt','w+');

tline = fgets(fid1);         % read input file line by line
idx=1;

while ischar(tline) %problem is in this line
    if size(tline,2)>73
        if strcmpi(tline(3:20), 'BOUNDARY GRID DATA')
            
            fprintf(fid2,'%s',tline);
            idx_start = idx
            chkstr = [tline '                                                  '];
            
            while ~strcmpi(chkstr(3:13),'SPOINT DATA')
                
                fprintf(fid2,'%s',tline);
                tline = fgets(fid1);
                idx = idx+1;
                chkstr = [tline '                                              '];
            end
        
            fprintf(fid2,'%s',tline);
            idx_end = idx
            break;break;break
        
        else
            
            tline = fgets(fid1);
            idx = idx+1;
        end
    else
        
        tline = fgets(fid1);
        idx = idx+1;
    end
end

fclose(fid1);
fclose(fid2);

I know I'm close, but fgets continues to return -1 where I noted the problem is. I know that means the end of the file has been reached, but I'm not sure how to fix that.

Answer 1

[Image Analyst]

Why not simply use fileread to suck up the whole file into a single string, then use strfind() to find the starting and ending indexes

str = fileread(filename)
index1 = strfind(str, 'BOUNDARY GRID DATA');
index2 = strfind(str, 'SPOINT  DATA'
outputString = str(index1:index2);

[Zain]

Worked perfectly thank you!

Answer 2

[Damir]

A PDF file explaining extraction you have asked for :

https://www.w-app.net/CV/Prolog/E1/

[Image Analyst]

Unless he wants to translate from Prolog I think you'll have to explain how to run Prolog code from within MATLAB.

Answer 3

[Damir]

No, this was not MATLAB related answer.

Just data extraction.