dup2.c

/*
 * Public domain dup2() lookalike
 * by Curtis Jackson @ AT&T Technologies, Burlington, NC
 * electronic address: burl!rcj
 *
 * dup2 performs the following functions:
 *
 * Check to make sure that fd1 is a valid open file descriptor.
 * Check to see if fd2 is already open; if so, close it.
 * Duplicate fd1 onto fd2; checking to make sure fd2 is a valid fd.
 * Return fd2 if all went well; return BADEXIT otherwise.
 */

#include<errno.h>// errno
#include<fcntl.h>// fcntl()
#include<unistd.h>// close()

#defineBADEXIT -1

int
dup2(intfd1, intfd2)
{
if (fd1!=fd2) {
#ifdefF_DUPFD
if (fcntl(fd1, F_GETFL) <0)
returnBADEXIT;
if (fcntl(fd2, F_GETFL) >= 0)
close(fd2);
if (fcntl(fd1, F_DUPFD, fd2) <0)
returnBADEXIT;
#else
errno=ENOTSUP;
returnBADEXIT;
#endif
 }
returnfd2;
}