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28 .\" @(#)dup.2 8.1 (Berkeley) 6/4/93
37 .Nd duplicate an existing file descriptor
45 .Fn dup2 "int oldd" "int newd"
50 duplicates an existing object descriptor and returns its value to
57 is a small non-negative integer index in
58 the per-process descriptor table.
59 The value must be less
60 than the size of the table, which is returned by
62 The new descriptor returned by the call
63 is the lowest numbered descriptor
64 currently not in use by the process.
66 The object referenced by the descriptor does not distinguish
76 are duplicate references to an open
82 calls all move a single pointer into the file,
83 and append mode, non-blocking I/O and asynchronous I/O options
84 are shared between the references.
85 If a separate pointer into the file is desired, a different
86 object reference to the file must be obtained by issuing an
90 The close-on-exec flag on the new file descriptor is unset.
94 the value of the new descriptor
97 If this descriptor is already in use and
101 the descriptor is first deallocated as if the
103 system call had been used.
106 is not a valid descriptor, then
115 is a valid descriptor, then
117 is successful, and does nothing.
119 The value -1 is returned if an error occurs in either call.
120 The external variable
122 indicates the cause of the error.
128 system calls fail if:
136 is not a valid active descriptor
138 Too many descriptors are active.
144 .Xr getdtablesize 2 ,
154 system calls are expected to conform to
161 functions appeared in