V4/usr/man/man2/open.2

Find at most related files.
including files from this version of Unix. 
.th OPEN II 8/5/73
.sh NAME
open \*- open for reading or writing
.sh SYNOPSIS
(open = 5.)
.br
.ft B
sys open; name; mode
.s3
open(name, mode)
.br
char *name;
.ft R
.sh DESCRIPTION
.it Open
opens the file
.it name
for reading
(if
.it mode
is 0),
writing (if
.it mode
is 1) or for both reading and writing
(if
.it mode
is 2).
.it Name
is the address of a string of ASCII characters representing
a path name, terminated by a null character.
.s3
The returned file descriptor should be saved for subsequent calls
to
.it read,
.it write,
and
.it close.
.sh "SEE ALSO"
creat(II), read(II), write(II), close(II)
.sh DIAGNOSTICS
The error bit
(c-bit) is set 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 10 files are open.
From C, a \*-1 value is returned on an error.