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       write - write to a file descriptor


       #include <unistd.h>

       ssize_t write(int fd, const void *buf, size_t count);


       write()  writes  up  to  count bytes from the buffer pointed buf to the
       file referred to by the file descriptor fd.

       The number of bytes written may be less than  count  if,  for  example,
       there  is  insufficient space on the underlying physical medium, or the
       RLIMIT_FSIZE resource limit is encountered (see setrlimit(2)),  or  the
       call was interrupted by a signal handler after having written less than
       count bytes.  (See also pipe(7).)

       For a seekable file (i.e., one to which lseek(2) may  be  applied,  for
       example,  a  regular  file)  writing  takes  place  at the current file
       offset, and the file offset is  incremented  by  the  number  of  bytes
       actually  written.   If  the file was open(2)ed with O_APPEND, the file
       offset is first set to  the  end  of  the  file  before  writing.   The
       adjustment  of the file offset and the write operation are performed as
       an atomic step.

       POSIX requires that a read(2) which can be  proved  to  occur  after  a
       write()  has  returned  returns  the  new data.  Note that not all file
       systems are POSIX conforming.


       On success, the number of bytes written  is  returned  (zero  indicates
       nothing  was  written).   On  error,  -1  is returned, and errno is set

       If count is zero and fd refers to a  regular  file,  then  write()  may
       return  a failure status if one of the errors below is detected.  If no
       errors are detected, 0 will  be  returned  without  causing  any  other
       effect.   If count is zero and fd refers to a file other than a regular
       file, the results are not specified.


       EAGAIN The file descriptor fd refers to a file other than a socket  and
              has  been  marked  nonblocking (O_NONBLOCK), and the write would

              The file descriptor fd refers to a socket and  has  been  marked
              nonblocking   (O_NONBLOCK),   and   the   write   would   block.
              POSIX.1-2001 allows either error to be returned for  this  case,
              and  does not require these constants to have the same value, so
              a portable application should check for both possibilities.

       EBADF  fd is not a valid file descriptor or is not open for writing.

              fd refers to a datagram socket for which a peer address has  not
              been set using connect(2).

       EFAULT buf is outside your accessible address space.

       EFBIG  An   attempt   was  made  to  write  a  file  that  exceeds  the
              implementation-defined maximum file size or the  process's  file
              size  limit,  or to write at a position past the maximum allowed

       EINTR  The call was  interrupted  by  a  signal  before  any  data  was
              written; see signal(7).

       EINVAL fd  is attached to an object which is unsuitable for writing; or
              the file was opened with  the  O_DIRECT  flag,  and  either  the
              address  specified  in buf, the value specified in count, or the
              current file offset is not suitably aligned.

       EIO    A low-level I/O error occurred while modifying the inode.

       ENOSPC The device containing the file referred to by fd has no room for
              the data.

       EPIPE  fd is connected to a pipe or socket whose reading end is closed.
              When this happens  the  writing  process  will  also  receive  a
              SIGPIPE  signal.   (Thus, the write return value is seen only if
              the program catches, blocks or ignores this signal.)

       Other errors may occur, depending on the object connected to fd.


       SVr4, 4.3BSD, POSIX.1-2001.

       Under SVr4 a write may be interrupted and return EINTR  at  any  point,
       not just before any data is written.


       A  successful return from write() does not make any guarantee that data
       has been committed to disk.  In fact, on some buggy implementations, it
       does  not  even guarantee that space has successfully been reserved for
       the data.  The only way to be sure is to call fsync(2)  after  you  are
       done writing all your data.

       If  a  write()  is interrupted by a signal handler before any bytes are
       written, then the call fails with the error EINTR; if it is interrupted
       after  at  least  one  byte  has  been  written, the call succeeds, and
       returns the number of bytes written.


       close(2), fcntl(2), fsync(2), ioctl(2), lseek(2),  open(2),  pwrite(2),
       read(2), select(2), writev(2), fwrite(3)


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