1/*
2 * Public domain dup2() lookalike
3 * by Curtis Jackson @ AT&T Technologies, Burlington, NC
4 * electronic address:  burl!rcj
5 *
6 * dup2 performs the following functions:
7 *
8 * Check to make sure that fd1 is a valid open file descriptor.
9 * Check to see if fd2 is already open; if so, close it.
10 * Duplicate fd1 onto fd2; checking to make sure fd2 is a valid fd.
11 * Return fd2 if all went well; return BADEXIT otherwise.
12 */
13
14#include <fcntl.h>
15#include <unistd.h>
16
17#define BADEXIT -1
18
19int
20dup2(int fd1, int fd2)
21{
22	if (fd1 != fd2) {
23		if (fcntl(fd1, F_GETFL) < 0)
24			return BADEXIT;
25		if (fcntl(fd2, F_GETFL) >= 0)
26			close(fd2);
27		if (fcntl(fd1, F_DUPFD, fd2) < 0)
28			return BADEXIT;
29	}
30	return fd2;
31}
32