File pointer is at the beginning of the file. A for append Opens an existing file. File pointer is at the end of the file. W for write. Creates a new file or truncates an existing file of the same name.
File pointer is at the beginning of the file.
It is possible to read from a file opened in 'W' or 'A' mode and it is possible to write to a file opened in 'R' mode. Writing to an existing file with the pointer located at its beginning will overwrite existing data. AmigaDOS allows for different levels of access protection for opened files. ARexx uses two of those levels.