DUP2(3C)                             SysV                             DUP2(3C)



NAME
     dup2 - duplicate an open file descriptor

SYNOPSIS
     int dup2 (fildes, fildes2)
     int fildes, fildes2;

DESCRIPTION
     The dup2 function provides an alternate interface to the service provided
     by the fcntl(2) function using the F_DUPFD command.

     fildes is a file descriptor referring to an open file, and fildes2 is a
     non-negative integer less than NOFILES. dup2 causes fildes2 to refer to
     the same file as fildes. If fildes2 already referred to an open file, it
     is closed first.

     The call:

          fid = dup2 (fildes, fildes2);

     is equivalent to:

          close (fildes2);
          fid= fcntl(fildes, F_DUPFD, fildes2);

     except for the following:

          If fildes2 is less than 0 or greater than or equal to {OPEN_MAX},
          dup2 returns -1 with errno set to [EBADF].

          If fildes is a valid file descriptor and is equal to fildes2, dup2
          returns fildes2 without closing it.

          If fildes is not a valid file descriptor, dup2 returns -1 and does
          not close fildes2. The value returned is equal to the value of
          fildes2 upon successful completion or -1 upon failure.

ERRORS
     dup2 fails if:

     [EBADF]        fildes is not a valid open file descriptor.

     [EMFILE]       NOFILES file descriptors are currently open.

     dup2           also fails if:

     [EINTR]        The dup2 function was terminated prematurely by a signal.

SEE ALSO
     creat(2), close(2), exec(2), fcntl(2), open(2), pipe(2), lockf(3C).

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