tail in C, available under the ISC license

svans.c

/*
 * Copyright (c) 2018  Joachim Nilsson <[email protected]>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#include <err.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>

int main(int argc, char *argv[])
{
	int fd;

	if (argc < 2)
		return 1;

	fd = open(argv[1], O_RDONLY | O_NONBLOCK);
	if (fd < 0)
		err(1, "Failed opening %s", argv[1]);
	
	while (1) {
		struct pollfd pfd = {
			.fd = fd,
			.events = POLLIN
		};
		ssize_t num;
		char buf[80];
		int rc;

		rc = poll(&pfd, 1, 1000);
		if (rc < 0) {
			warn("poll");
			sleep(1);
			continue;
		}
		if (rc == 0) {
			warn("timeout");
			continue;
		}

		num = read(fd, buf, sizeof(buf));
		if (!num) {
			sleep(1);
			continue;
		}
		if (num < 0) {
			warn("read failed");
			continue;
		}
		num = write(STDOUT_FILENO, buf, num);
	}

	return 0;
}