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Plan 9 - man page for open (plan9 section 2)

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OPEN(2) 										  OPEN(2)

       open, create, close - open a file for reading or writing, create file

       #include <u.h>
       #include <libc.h>

       int open(char *file, int omode)

       int create(char *file, int omode, ulong perm)

       int close(int fd)

       Open  opens  the  file for I/O 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 a copy  of  the	file  descriptor).   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 con-
       taining directory.  If the file already exists, it is truncated to 0 length, and the  per-
       missions, owner, and group remain unchanged.  The created file is a directory if the CHDIR
       bit is set in omode.  It is an exclusive-use file if the CHEXCL bit is  set.   Such  files
       may  be	open  for  I/O	by  only one client at a time, but the file descriptor may become
       invalid if no I/O is done for an extended period; see open(5).

       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 automatically upon termination of a process; close allows the  file  descriptor
       to be reused.


       intro(2), bind(2), stat(2)

       These functions set errstr.

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