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RedHat 9 (Linux i386) - man page for dup (redhat section 2)

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

       dup, dup2 - duplicate a file descriptor

       #include <unistd.h>

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

       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 inter-
       changeably. 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.

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

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

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

       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.

       SVr4, SVID, POSIX, X/OPEN, BSD 4.3. SVr4 documents additional EINTR and ENOLINK error con-
       ditions.  POSIX.1 adds EINTR.

       fcntl(2), open(2), close(2)

Linux 1.1.46				    1994-08-21					   DUP(2)
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