y=exist otherwise run & scan

.MODEL SMALL
.STACK 100H
.DATA
.CODE
MAIN PROC

    MOV BL,'0'

    WHILE:
    MOV AH,1
    INT 21H
    MOV BL,AL
    CMP BL,59H
    JE END_IF

    JMP WHILE
    END_IF:


    MAIN ENDP
END MAIN