fd_copy - duplicate a descriptor

#include <fd.h>

int fd_copy(to,from);

int to;
int from;

fd_copy copies descriptor from to descriptor to. If to was already open, fd_copy closes it. fd_copy always leaves from intact; if to and from are the same number, fd_copy does nothing.

fd_copy returns 0 on success, -1 on error. fd_copy does not guarantee that to will remain open, if it was open, in case of error.

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