man(1) Manual page archive

     READ(2)                                                   READ(2)

          read - read from file

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

          Read causes data to be read from the open file associated
          with the file descriptor.  Buffer is the location of nbytes
          contiguous bytes into which the input will be placed.  It is
          not guaranteed that all nbytes bytes will be read; for exam-
          ple if the file refers to a terminal at most one line will
          be returned.  In any event the number of characters read is

          A return value of 0 is conventionally interpreted as end of
          file.  If more data is subsequently written on the open file
          by another process, then a further read will return it.

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

          As mentioned, 0 is returned when the end of the file has
          been reached.  If the read was otherwise unsuccessful the
          return value is -1.  Many conditions can generate an error:
          physical I/O errors, bad buffer address, preposterous
          nbytes, file descriptor not that of an input file.