open \- open for reading or writing
is 1) or for both reading and writing
is the address of a string of ASCII characters representing
a path name, terminated by a null character.
The file is positioned at the beginning (byte 0).
The returned file descriptor must be used for subsequent calls
for other input-output functions on the file.
creat(2), read(2), write(2), dup(2), close(2)
The value \-1 is returned
if the file does not exist,
if one of the necessary directories
does not exist or is unreadable, if the file is not
readable (resp. writable), or if too many files are open.