Append in file in Assembly

Following is the program to append in a file in Assembly language.

TITLE Append in file in Assembly Language
.model small
.stack

.data
file db "myfile.txt",0
msg db "This is a program to append in file in Assembly language.",'$'

.code
start:
main proc
mov ax,@data
mov ds,ax

;load file handler
mov dx,offset file
mov al,1
mov ah,3dh
int 21h

;Appending File
mov bx,ax
mov cx,0
mov ah,42h
mov al,02h
int 21h

;Writing File
mov cx,lengthof msg; should have been 1 less than length of msg.
mov dx,offset msg
mov ah,40h
int 21h

;close file
mov ah,3eh
int 21h

;exit
mov ax,4c00h
int 21h
main endp
end start
end

Read from file Assembly Language

.model small
.stack
.data
buffer db 5000 dup("$")
file db "myfile.txt",0


.code
mov ax,@data
mov ds,ax
 
mov dx, offset file
mov al,0            ;Open file (read-Only)
;mov al,1            ; Write only
;mov al,2            ; Read & Write
mov ah,3dh           ; Load File handler and store in ax
int 21h

mov bx,ax            ; Move file Handler to bx
mov dx,offset buffer
mov ah,3fh
int 21h

mov ah,9h
int 21h

mov ah,4ch
int 21h
end