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 
19 int
dup2(int fd1,int fd2)20 dup2(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