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v0.5.1
https://github.com/python/cpython
09 December 2020, 11:06:31 UTC
Revision 094183ebeb1d539d71e9da9be8cee12ee7db972f authored by Guido van Rossum on 15 February 1994, 16:04:53 UTC, committed by Guido van Rossum on 15 February 1994, 16:04:53 UTC 
At the release of 1.0.1.
1 parent c5c67bc
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Tip revision: 094183ebeb1d539d71e9da9be8cee12ee7db972f authored by Guido van Rossum on 15 February 1994, 16:04:53 UTC
At the release of 1.0.1.
Tip revision: 094183e
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 <fcntl.h>

#define BADEXIT -1

int
dup2(fd1, fd2)
int fd1, fd2;
{
	if (fd1 != fd2) {
		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;
	}
	return fd2;
}
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