access file in mips using mars tool - mips

Question

I'm trying to do some access on file using mips instruction.
I want to read file line by line not all of the file at a time so this code(1) does not work.
Also I want to write to the file and not overwrite!
Can any one help me?
Code:
Open a file for writing
li $v0, 13 # system call for open file
la $a0, file # board file name
li $a1, 0 # Open for reading
li $a2, 0
syscall # open a file (file descriptor returned in $v0)
move $s6, $v0 # save the file descriptor
Read from file
li $v0, 14 # system call for read from file
move $a0, $s6 # file descriptor
la $a1, buffer # address of buffer to which to read
li $a2, 40 # hardcoded buffer length
syscall # read from file
Close the file
li $v0, 16 # system call for close file
move $a0, $s6 # file descriptor to close
syscall # close file

Answer 1

I want to read file line by line not all of the file at a time so this code(1) does not work.
Read chunks of data into a buffer (e.g. a few kilobytes). Then process that buffer line-by-line (by looking for linefeed characters), and read more data from the file when you've reached the end of the buffer.
Also I want to write to the file and not overwrite!
Set the flags ($a1) to 9 when opening the file (syscall 13). This corresponds to "write-only with create and append" (see this MARS syscall reference).

Answer 2

it's work thx alot :)
.data
fin: .asciiz "file.txt" # filename for input
buffer: .space 128
buffer1: .asciiz "\n"
val : .space 128
.text
################################################ fileRead:
# Open file for reading
li $v0, 13 # system call for open file
la $a0, fin # input file name
li $a1, 0 # flag for reading
li $a2, 0 # mode is ignored
syscall # open a file
move $s0, $v0 # save the file descriptor
# reading from file just opened
li $v0, 14 # system call for reading from file
move $a0, $s0 # file descriptor
la $a1, buffer # address of buffer from which to read
li $a2, 6 # hardcoded buffer length
syscall # read from file
li $v0, 4 #
la $a0, buffer # buffer contains the values
syscall # print int
lb $t1 , buffer
# reading from file just opened
li $v0, 14 # system call for reading from file
move $a0, $s0 # file descriptor
la $a1, buffer # address of buffer from which to read
li $a2, 6 # hardcoded buffer length
syscall # read from file
li $v0, 4 #
la $a0, buffer # buffer contains the values
syscall # print int
## sh $t5 , val($0) #sw $t5, theArray($t0)
# Close the file
li $v0, 16 # system call for close file
move $a0, $s6 # file descriptor to close
syscall # close file