OPEN(2)
NAME
open, create, close − open a file for reading or writing, create file
SYNOPSIS
int open(char ∗file, int omode)
int create(char ∗file, int omode, ulong perm)
int close(int fd)
DESCRIPTION
Open opens the file and returns an associated file descriptor. Omode is one of OREAD, OWRITE, ORDWR, or OEXEC, asking for permission to read, write, read and write, or execute, respectively. In addition, there are three values that can be ORed with the omode: OTRUNC says to truncate the file to zero length before opening it; OCEXEC says to close the file when an exec(2) or execl system call is made; and ORCLOSE says to remove the file when it is closed (by everyone who has it open). The omode values are defined in <libc.h>. Open fails if the file does not exist or the user does not have permission to open it for the requested purpose (see stat(2) for a description of permissions). The user must have write permission on the file if the OTRUNC bit is set. For the open system call (unlike the implicit open in exec(2)), OEXEC is actually identical to OREAD.
Create creates a new file or prepares to rewrite an existing file, opens it according to omode (as described for open), and returns an associated file descriptor. If the file is new, the owner is set to the userid of the creating process group; the group to that of the containing directory; the permissions to perm ANDed with the permissions of the containing directory. If the file already exists, it is truncated to 0 length, and the permissions, owner, and group remain unchanged. The created file is a directory if the CHDIR bit is set in omode. Create fails if the path up to the last element of file cannot be evaluated, if the user doesn’t have write permission in the final directory, or if the file already exists and does not permit the access defined by omode. If the file is new and the directory in which it is created is a union directory (see intro(2)) then the constituent directory where the file is created depends on the structure of the union: see bind(2).
Close closes the file associated with a file descriptor. Provided the file descriptor is a valid open descriptor, close is guaranteed to close it; there will be no error. Files are closed upon termination of a process; close allows the file descriptor to be reused.
SEE ALSO
DIAGNOSTICS
These functions set errstr.
Plan 9 — January 03, 1993