Open open a file for read/write access open char *fname int mode os9 I$OPEN This call opens an existing file for reading if "mode" is 1, writing if "mode" is 2, or reading and writing if "mode" is 3. NOTE that these values are OS-9 specific and not compatible with other systems. "Fname" should point to a string representing the pathname of the file. Open returns an integer as "path number" which should be used by i/o system calls referring to the file. The position where reads or writes start is at the beginning of the file. -1 is returned if the file does not exist, if the pathname cannot be searched, if too many files are already open, or if the file permissions deny the requested mode. creat(), read(), write(), dup(), close()