;Open a file handle
mov ax, 3Dh
mov dx, offset filename
int 21h
;Check that the file handle is valid
cmp ax, 0
jne file_open
;Start looping through the directory
mov si, offset directory
mov di, offset filename
loop:
mov al, [si]
cmp al, 0
je exit
;Copy the filename
mov [di], al
inc si
inc di
jmp loop
file_open:
;Read the file and search for "foo"
mov bx, ax
mov ah, 3Fh
mov cx, 0FFFFh
mov dx, offset buffer
int 21h
;Check if the end of file has been reached
cmp ax, 0
je exit
;Loop through the read buffer
mov si, offset buffer
mov di, offset replace
loop2: mov al, [si] cmp al, 'f' je check_foo inc si jmp loop2
check_foo: cmp byte [si + 1], 'o' jne loop2 cmp byte [si + 2], 'o' jne loop2
;Replace "foo" with "bar" mov [di], 'b' inc di mov [di], 'a' inc di mov [di], 'r' inc di jmp loop2
;Write the modified buffer to the file mov bx, ax mov ah, 40h mov cx, 0FFFFh mov dx, offset replace int 21h
;Go to the next file jmp file_open
exit: ;Close the file mov ah, 3Eh int 21h
;Exit mov ax, 4C00h int 21h
