open ... for ... as
Open a file stream.
Syntax:
open 
filename
 for 
mode
 as 
stream
filename
 is the file to be opened.
mode
 tell the computer what kind of operation you require on file.
stream is
represented by a number you assign to the opened file. You will pass
that number to other command in order to refer to the file.
Files can be opened in one of the following modes: input , output , append
Example:
' open a text file
open
 "myfile.txt" for  input as  1