dup(2)                              CLIX                              dup(2)



  NAME

    dup, dup2 - Duplicates an open file descriptor

  LIBRARY

    Standard C Library (libc.a)

  SYNOPSIS

    int dup(
      int fildes );

    int dup2(
      int old ,
      int new );

  PARAMETERS

    fildes   Specifies an open file descriptor to duplicate.

    old      Specifies an open file descriptor.

    new      Specifies an open file descriptor that is returned by the dup2()
             function.

  DESCRIPTION

    The fildes parameter is a file descriptor obtained from the creat(),
    open(), dup(), fcntl(), or pipe() functions.  The dup() function returns a
    new file descriptor having the following in common with the original:

    ⊕  Same open file (or pipe).

    ⊕  Same file pointer (that is, both file descriptors share one file
       pointer).

    ⊕  Same access mode (read, write or read/write).

    The new file descriptor is set to remain open across exec() functions.
    (See the fcntl() function.)

    The file descriptor returned is the lowest one available.

    The dup() and dup2() functions provide an alternate interface to the
    service provided by the fcntl() function using the F_DUPFD command.  The
    call:

    fid = dup (fildes);

    is equivalent to:



  2/94 - Intergraph Corporation                                              1

  dup(2)                              CLIX                              dup(2)



    fid = fcntl (fildes, F_DUPFD, 0);

    The call:

    fid = dup2 (old, new);

    is equivalent to:

    close (new);
    fid = fcntl (fildes, F_DUPFD, new);


  EXAMPLES

    To duplicate an existing file descriptor:

    new_fd = dup(existing_fd);
    if (new_fd == -1)
         perror("dup failed");


  RETURN VALUES

    Upon successful completion a non-negative integer (the file descriptor) is
    returned.  Otherwise, a value of -1 is returned and errno is set to
    indicate the error.

  ERRORS

    The dup() and dup2 functions fail if one or both of the following are
    true:

    [EBADF]     The old or fildes parameter is not a valid open file
                descriptor.

    [EMFILE]    The NOFILES (defined in master.d) file descriptors are
                currently open.

    [EINTR]     A signal was caught during the dup() functions.

    [ENOLINK]   The fildes parameter is on a remote machine and the link to
                that machine is no longer active.

  RELATED INFORMATION

    Functions:  close(2), creat(2), exec(2), fcntl(2), open(2), pipe(2),
    lockf(3)







  2                                              Intergraph Corporation - 2/94