man(1) Manual page archive

     WRITE(2)                                                 WRITE(2)

          write - write on a file

          write(fildes, buffer, nbytes)
          char *buffer;

          Write writes data on the open file associated with the file

          Buffer is the address of nbytes contiguous bytes which are
          written on the output file.  The number of characters actu-
          ally written is returned.  It should be regarded as an error
          if this is not the same as requested.

          If the open file is being read by another process, data of
          at most one write will be delivered to any read(2) in the
          other process.  In particular, if nbytes = 0, the read will
          return a count of 0, which is conventionally taken to mean
          end of file.

          Writes which are synchronized with file system blocks are
          more efficient than others; see filsys(5).

          On some systems 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 that he does not own.

          creat(2), open(2), pipe(2), select(2)

          Returns -1 on error: bad descriptor, buffer address, or
          count; physical I/O errors.