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 

    16 #define BADEXIT -1

    17 

    18 int

    19 dup2(int fd1, int fd2)

    20 {

    21 	if (fd1 != fd2) {

    22 		if (fcntl(fd1, F_GETFL) < 0)

    23 			return BADEXIT;

    24 		if (fcntl(fd2, F_GETFL) >= 0)

    25 			close(fd2);

    26 		if (fcntl(fd1, F_DUPFD, fd2) < 0)

    27 			return BADEXIT;

    28 	}

    29 	return fd2;

    30 }