cpython-withatomic / Python / 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

dup2(fd1, fd2)
int fd1, fd2;
	if (fd1 != fd2) {
		if (fcntl(fd1, F_GETFL) < 0)
			return BADEXIT;
		if (fcntl(fd2, F_GETFL) >= 0)
		if (fcntl(fd1, F_DUPFD, fd2) < 0)
			return BADEXIT;
	return fd2;
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