write man page on OpenBSD

Man page or keyword search:  
man Server   11362 pages
apropos Keyword Search (all sections)
Output format
OpenBSD logo
[printable version]

WRITE(2)		  OpenBSD Programmer's Manual		      WRITE(2)

     write, writev, pwrite, pwritev - write output

     #include <sys/types.h>
     #include <unistd.h>

     write(int d, const void *buf, size_t nbytes);

     pwrite(int d, const void *buf, size_t nbytes, off_t offset);

     #include <sys/types.h>
     #include <sys/uio.h>
     #include <unistd.h>

     writev(int d, const struct iovec *iov, int iovcnt);

     pwritev(int d, const struct iovec *iov, int iovcnt, off_t offset);

     write() attempts to write nbytes of data to the object referenced by the
     descriptor d from the buffer pointed to by buf.  writev() performs the
     same action, but gathers the output data from the iovcnt buffers
     specified by the members of the iov array: iov[0], iov[1], ...,
     iov[iovcnt-1].  pwrite() and pwritev() perform the same functions, but
     write to the specified position offset in the file without modifying the
     file pointer.

     For writev() and pwritev(), the iovec structure is defined as:

	   struct iovec {
		   void *iov_base;
		   size_t iov_len;

     Each iovec entry specifies the base address and length of an area in
     memory from which data should be written.	writev() and pwritev() will
     always write a complete area before proceeding to the next.

     On objects capable of seeking, the write() starts at a position given by
     the pointer associated with d (see lseek(2)).  Upon return from write(),
     the pointer is incremented by the number of bytes which were written.

     Objects that are not capable of seeking always write from the current
     position.	The value of the pointer associated with such an object is

     If the real user is not the superuser, then write() clears the set-user-
     ID bit on a file.	This prevents penetration of system security by a user
     who ``captures'' a writable set-user-ID file owned by the superuser.

     If write() succeeds it will update the st_ctime and st_mtime fields of
     the file's meta-data (see stat(2)).

     When using non-blocking I/O on objects such as sockets that are subject
     to flow control, write() and writev() may write fewer bytes than
     requested; the return value must be noted, and the remainder of the
     operation should be retried when possible.

     Note that writev() and pwritev() will fail if the value of iovcnt exceeds
     the constant IOV_MAX.

     Upon successful completion the number of bytes which were written is
     returned.	Otherwise, a -1 is returned and the global variable errno is
     set to indicate the error.

     write(), pwrite(), writev(), and pwritev() will fail and the file pointer
     will remain unchanged if:

     [EBADF]	   d is not a valid descriptor open for writing.

     [EPIPE]	   An attempt is made to write to a pipe that is not open for
		   reading by any process.

     [EPIPE]	   An attempt is made to write to a socket of type SOCK_STREAM
		   that is not connected to a peer socket.

     [EFBIG]	   An attempt was made to write a file that exceeds the
		   process's file size limit or the maximum file size.

     [EINVAL]	   The pointer associated with d was negative.

     [ENOSPC]	   There is no free space remaining on the file system
		   containing the file.

     [EDQUOT]	   The user's quota of disk blocks on the file system
		   containing the file has been exhausted.

     [EIO]	   An I/O error occurred while reading from or writing to the
		   file system.

     [EAGAIN]	   The file was marked for non-blocking I/O, and no data could
		   be written immediately.

     [EFAULT]	   Part of iov or buf points outside the process's allocated
		   address space.

     In addition, write() and pwrite() may return the following error:

     [EINVAL]	   nbytes was larger than SSIZE_MAX.

     pwrite() and pwritev() may return the following error:

     [ESPIPE]	   d is associated with a pipe, socket, or FIFO.

     writev() and pwritev() may return one of the following errors:

		   The destination is no longer available when writing to a
		   UNIX-domain datagram socket on which connect(2) had been
		   used to set a destination address.

     [EINVAL]	   iovcnt was less than or equal to 0, or greater than

     [EINVAL]	   The sum of the iov_len values in the iov array overflowed
		   an ssize_t.

     [ENOBUFS]	   The system lacked sufficient buffer space or a queue was

     fcntl(2), lseek(2), open(2), pipe(2), poll(2), select(2)

     The write() function conforms to IEEE Std 1003.1-1990 (``POSIX'').	 The
     writev() and pwrite() functions conform to X/Open Portability Guide Issue
     4.2 (``XPG4.2'').

     The pwritev() function call appeared in OpenBSD 2.7.  The pwrite()
     function call appeared in AT&T System V.4 UNIX.  The writev() function
     call appeared in 4.2BSD.  The write() function call appeared in Version 2
     AT&T UNIX.

     Error checks should explicitly test for -1.  Code such as

	   while ((nr = write(fd, buf, sizeof(buf))) > 0)

     is not maximally portable, as some platforms allow for nbytes to range
     between SSIZE_MAX and SIZE_MAX - 2, in which case the return value of an
     error-free write() may appear as a negative number distinct from -1.
     Proper loops should use

	   while ((nr = write(fd, buf, sizeof(buf))) != -1 && nr != 0)

OpenBSD 4.9		       December 30, 2009		   OpenBSD 4.9

List of man pages available for OpenBSD

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net