DUP(2)              Linux Programmer's Manual              DUP(2)

NAME
       dup, dup2 - duplicate a file descriptor

SYNOPSIS
       #include <unistd.h>

       int dup(int oldfd);
       int dup2(int oldfd, int newfd);

DESCRIPTION
       dup and dup2 create a copy of the file descriptor oldfd.

       The  old  and new descriptors may be used interchangeably.
       They share locks, file position pointers  and  flags;  for
       example,  if  the file position is modified by using lseek
       on one of the descriptors, the position  is  also  changed
       for the other.

       The  two  descriptors do not share the close-on-exec flag,
       however.

       dup uses the lowest-numbered unused descriptor for the new
       descriptor.

       dup2 makes newfd be the copy of oldfd, closing newfd first
       if necessary.

RETURN VALUE
       dup and dup2 return the new descriptor, or -1 if an  error
       occurred (in which case, errno is set appropriately).

ERRORS
       EBADF  oldfd  isn't  an  open file descriptor, or newfd is
              out of the allowed range for file descriptors.

       EMFILE The process already has the maximum number of  file
              descriptors open and tried to open a new one.

WARNING
       The  error  returned by dup2 is different to that returned
       by fcntl(...,F_DUPFD,...)  when newfd is out of range.  On
       some  systems  dup2  also  sometimes  returns  EINVAL like
       F_DUPFD.

CONFORMING TO
       SVr4, SVID, POSIX, X/OPEN, BSD 4.3. SVr4  documents  addi-
       tional  EINTR  and ENOLINK error conditions.  POSIX.1 adds
       EINTR.

SEE ALSO
        fcntl (2), open (2), close (2).

Linux 1.1.46              21 August 1994                        1