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 <errno.h>
15 #include <fcntl.h>
16 #include <unistd.h>
17 
18 #define BADEXIT -1
19 
20 int
dup2(int fd1,int fd2)21 dup2(int fd1, int fd2)
22 {
23     if (fd1 != fd2) {
24 #ifdef F_DUPFD
25         if (fcntl(fd1, F_GETFL) < 0)
26             return BADEXIT;
27         if (fcntl(fd2, F_GETFL) >= 0)
28             close(fd2);
29         if (fcntl(fd1, F_DUPFD, fd2) < 0)
30             return BADEXIT;
31 #else
32         errno = ENOTSUP;
33         return BADEXIT;
34 #endif
35     }
36     return fd2;
37 }
38