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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*      $OpenBSD: cmp.c,v 1.12 2009/10/27 23:59:36 deraadt Exp $      */
/*      $NetBSD: cmp.c,v 1.7 1995/09/08 03:22:56 tls Exp $      */

/*
 * Copyright (c) 1987, 1990, 1993, 1994
 *	The 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 <sys/types.h>
#include <sys/stat.h>

#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <locale.h>

#include "extern.h"

int	lflag, sflag;

static void usage(void);

int
main(int argc, char *argv[])
{
	struct stat sb1, sb2;
	off_t skip1, skip2;
	int ch, fd1, fd2, special;
	char *file1, *file2;

	setlocale(LC_ALL, "");

	while ((ch = getopt(argc, argv, "ls")) != -1)
		switch (ch) {
		case 'l':		/* print all differences */
			lflag = 1;
			break;
		case 's':		/* silent run */
			sflag = 1;
			break;
		case '?':
		default:
			usage();
		}

	argv += optind;
	argc -= optind;

	if (lflag && sflag)
		errx(ERR_EXIT, "only one of -l and -s may be specified");

	if (argc < 2 || argc > 4)
		usage();

	/* Backward compatibility -- handle "-" meaning stdin. */
	special = 0;
	if (strcmp(file1 = argv[0], "-") == 0) {
		special = 1;
		fd1 = 0;
		file1 = "stdin";
	} else if ((fd1 = open(file1, O_RDONLY, 0)) < 0) {
		if (sflag)
			exit(ERR_EXIT);
		else
			err(ERR_EXIT, "%s", file1);
	}
	if (strcmp(file2 = argv[1], "-") == 0) {
		if (special) {
			if (sflag)
				exit(ERR_EXIT);
			else
				errx(ERR_EXIT,
					"standard input may only be specified once");
		}
		special = 1;
		fd2 = 0;
		file2 = "stdin";
	} else if ((fd2 = open(file2, O_RDONLY, 0)) < 0) {
		if (sflag)
			exit(ERR_EXIT);
		else
			err(ERR_EXIT, "%s", file2);
	}

	skip1 = argc > 2 ? strtoq(argv[2], NULL, 0) : 0;
	skip2 = argc == 4 ? strtoq(argv[3], NULL, 0) : 0;

	if (!special) {
		if (fstat(fd1, &sb1)) {
			if (sflag)
				exit(ERR_EXIT);
			else
				err(ERR_EXIT, "%s", file1);
		}
		if (!S_ISREG(sb1.st_mode))
			special = 1;
		else {
			if (fstat(fd2, &sb2)) {
				if (sflag)
					exit(ERR_EXIT);
				else
					err(ERR_EXIT, "%s", file2);
			}
			if (!S_ISREG(sb2.st_mode))
				special = 1;
		}
	}

	if (special)
		c_special(fd1, file1, skip1, fd2, file2, skip2);
	else
		c_regular(fd1, file1, skip1, sb1.st_size,
		    fd2, file2, skip2, sb2.st_size);
	return 0;
}

static void
usage(void)
{

	(void)fprintf(stderr,
	    "usage: cmp [-l | -s] file1 file2 [skip1 [skip2]]\n");
	exit(ERR_EXIT);
}