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Minix/CD-ROM-2.0/MINIX/MANUALS/CAT2/DUP.2

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+DUP(2)                    Minix Programmer's Manual                     DUP(2)
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+
+NAME
+     dup, dup2 - duplicate a descriptor
+
+SYNOPSIS
+     #include <unistd.h>
+
+     int dup(int oldd)
+     int dup2(int oldd, int newd)
+
+DESCRIPTION
+     Dup duplicates an existing descriptor.  The argument oldd is a small non-
+     negative  integer  index  in the per-process descriptor table.  The value
+     must be less than OPEN_MAX, the size of the table.   The  new  descriptor
+     returned  by  the  call,  let's  name  it  newd,  is  the lowest numbered
+     descriptor that is not currently in use by the process.
+
+     The object referenced by the  descriptor  does  not  distinguish  between
+     references  using  oldd  and  newd in any way.  Thus if newd and oldd are
+     duplicate references to an open  file,  read(2),  write(2)  and  lseek(2)
+     calls  all  move  a  single  pointer into the file, and append mode, non-
+     blocking  I/O  and  asynchronous  I/O  options  are  shared  between  the
+     references.   If a separate pointer into the file is desired, a different
+     object reference to the file must be obtained by  issuing  an  additional
+     open(2)  call.   The  close-on-exec  flag  on  the new file descriptor is
+     unset.
+
+     In the second form of the call, the value of newd desired  is  specified.
+     If this descriptor is already in use, the descriptor is first deallocated
+     as if a close(2) call had been done first.  Newd  is  not  closed  if  it
+     equals oldd.
+
+RETURN VALUE
+     The value -1 is returned if an error occurs in either call.  The external
+     variable errno indicates the cause of the error.
+
+ERRORS
+     Dup and dup2 fail if:
+
+     [EBADF]        Oldd or newd is not a valid active descriptor
+
+     [EMFILE]       Too many descriptors are active.
+
+NOTES
+     Dup and dup2 are now implemented using the F_DUPFD function of  fcntl(2),
+     although  the  old  system  call  interfaces  still  exist to support old
+     programs.
+
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+4BSD                              May 13, 1986                               1
+
+
+
+DUP(2)                    Minix Programmer's Manual                     DUP(2)
+
+
+SEE ALSO
+     open(2), close(2), fcntl(2), pipe(2).
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+4BSD                              May 13, 1986                               2
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