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Fix a 37 year old bug introduced by Bill Joy on August 24, 1977
that was already present in the 1BSD release on March 9, 1978
by merging Keith Bostic's 22 year old fix from 4.4BSD (not kidding).

Original CSRG SCCS commit message:

  ^As 00009/00006/00145
  ^Ad D 5.7 92/03/04 14:35:42 bostic 9 8
  ^Ac can't use freopen; example is "date | head file1 /dev/stdin"

ok deraadt@ tedu@, also checked by Martin <Natano dot net>

/*	$OpenBSD: head.c,v 1.18 2014/10/08 08:31:53 schwarze Exp $	*/

/*
 * Copyright (c) 1980, 1987 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <limits.h>
#include <err.h>
#include <errno.h>
#include <unistd.h>

static void usage(void);

/*
 * head - give the first few lines of a stream or of each of a set of files
 *
 * Bill Joy UCB August 24, 1977
 */

int
main(int argc, char *argv[])
{
	FILE	*fp;
	long 	cnt;
	int	ch, firsttime;
	long	linecnt = 10;
	char	*p = NULL;
	int	status = 0;

	/* handle obsolete -number syntax */
	if (argc > 1 && argv[1][0] == '-' &&
	    isdigit((unsigned char)argv[1][1])) {
		p = argv[1] + 1;
		argc--;
		argv++;
	}

	while ((ch = getopt(argc, argv, "n:")) != -1) {
		switch (ch) {
		case 'n':
			p = optarg;
			break;
		default:
			usage();	
		}
	}
	argc -= optind, argv += optind;

	if (p) {
		const char *errstr;

		linecnt = strtonum(p, 1, LONG_MAX, &errstr);
		if (errstr)
			errx(1, "line count %s: %s", errstr, p);
	}

	for (firsttime = 1; ; firsttime = 0) {
		if (!*argv) {
			if (!firsttime)
				exit(status);
			fp = stdin;
		} else {
			if ((fp = fopen(*argv, "r")) == NULL) {
				warn("%s", *argv++);
				status = 1;
				continue;
			}
			if (argc > 1) {
				if (!firsttime)
					putchar('\n');
				printf("==> %s <==\n", *argv);
			}
			++argv;
		}
		for (cnt = linecnt; cnt && !feof(fp); --cnt)
			while ((ch = getc(fp)) != EOF)
				if (putchar(ch) == '\n')
					break;
		fclose(fp);
	}
	/*NOTREACHED*/
}


static void
usage(void)
{
	fputs("usage: head [-count | -n count] [file ...]\n", stderr);
	exit(1);
}