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3.12

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dup2.c

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/*

* 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>

#include <fcntl.h>

#include <unistd.h>

#define BADEXIT -1

int

dup2(int fd1, int fd2)

{

if (fd1 != fd2) {

#ifdef F_DUPFD

if (fcntl(fd1, F_GETFL) < 0)

return BADEXIT;

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

close(fd2);

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

return BADEXIT;

#else

errno = ENOTSUP;

return BADEXIT;

#endif

}

return fd2;

}