dup

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.

       After successful return of dup or dup2, 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 neces-
       sary.

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 additional EINTR and
       ENOLINK error conditions.  POSIX.1 adds EINTR.

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



Linux 1.1.46                      1994-08-21                            DUP(2)