V7/usr/src/libc/gen/isatty.c

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/*
 * Returns 1 iff file is a tty
 */

#include <sgtty.h>

isatty(f)
{
	struct sgttyb ttyb;

	if (gtty(f, &ttyb) < 0)
		return(0);
	return(1);
}