working with files

I'm trying to make something similar to the grep tool, loop through a file trying to get the line(word) that matches my string. I have this code so far:

Code:

format PE GUI

entry start

include 'win32ax.inc'

.data
        fileName db 'file.txt',0
        fHandle  dd 0
        fSize    dd 0
        fSpace   dd 0
        asBytesRead dd 0
        
.code

start:
        ;Open File
        invoke CreateFile, fileName, GENERIC_READ, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0
        cmp eax, INVALID_HANDLE_VALUE
        je show_error
        mov [fHandle], eax

        invoke GetFileSize, [fHandle], 0
        cmp eax, 0ffffffffh 
        je show_error
        mov [fSize], eax
        
        invoke GlobalAlloc, GMEM_FIXED, [fSize]
        test   eax, eax 
        jz     show_error
        mov    [fSpace], eax 

        invoke ReadFile, [fHandle], [fSpace], [fSize], asBytesRead, 0 ;needs lpNumberOfBytesRead 
        test   eax, eax 
        jz     show_error
        
        invoke MessageBox, 0, [fSpace], 0, 0 ;show contents of file 

        
        jmp finish
        
show_error:
        invoke MessageBox, 0, "Error!", "Error!", MB_OK

finish:
        invoke CloseHandle, [fHandle] ;Close File
        invoke ExitProcess, 0
        
section '.idata' import data readable writeable

        library kernel32,'KERNEL32.DLL', user32,'USER32.DLL'
        
        include 'api/kernel32.inc'
        include 'api/user32.inc'

My problem is that I dont know how to loop through the file line by line to get the ones that match.

I've written a DOS version too, but, I have the same problem (I dont know how to loop through the lines) and also when the file is big it doesnt open it (maybe cause its running on 16 bits mode).

Thanks a lot for your help!