dup – duplicate an open file descriptor|
int dup(int oldfd, int newfd)
Given a file descriptor, oldfd, referring to an open file, dup
returns a new file descriptor referring to the same file. |
If newfd is –1 the system chooses the lowest available file descriptor. Otherwise, dup will use newfd for the new file descriptor (closing any old file associated with newfd). File descriptors are allocated dynamically, so to prevent unwarranted growth of the file descriptor table, dup requires that newfd be no greater than 20 more than the highest file descriptor ever used by the program.
Dup does not copy the per file descriptor OCEXEC flag, meaning
that newfd will not be closed on exec(2) syscall, when oldfd had
been previously opend with it.