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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: tail.c,v 1.17 2009/10/27 23:59:44 deraadt Exp $	*/

/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Edward Sze-Tyan Wang.
 *
 * 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 <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

int fflag, rflag, rval;
char *fname;
int is_stdin;

static void obsolete(char **);
static void usage(void);

int
main(int argc, char *argv[])
{
	struct stat sb;
	FILE *fp;
	off_t off = 0;
	enum STYLE style;
	int ch, first;
	char *p;

	/*
	 * Tail's options are weird.  First, -n10 is the same as -n-10, not
	 * -n+10.  Second, the number options are 1 based and not offsets,
	 * so -n+1 is the first line, and -c-1 is the last byte.  Third, the
	 * number options for the -r option specify the number of things that
	 * get displayed, not the starting point in the file.  The one major
	 * incompatibility in this version as compared to historical versions
	 * is that the 'r' option couldn't be modified by the -lbc options,
	 * i.e. it was always done in lines.  This version treats -rc as a
	 * number of characters in reverse order.  Finally, the default for
	 * -r is the entire file, not 10 lines.
	 */
#define	ARG(units, forward, backward) {					\
	if (style)							\
		usage();						\
	off = strtoll(optarg, &p, 10) * (units);			\
	if (*p)								\
		errx(1, "illegal offset -- %s", optarg);		\
	switch(optarg[0]) {						\
	case '+':							\
		if (off)						\
			off -= (units);					\
			style = (forward);				\
		break;							\
	case '-':							\
		off = -off;						\
		/* FALLTHROUGH */					\
	default:							\
		style = (backward);					\
		break;							\
	}								\
}

	obsolete(argv);
	style = NOTSET;
	while ((ch = getopt(argc, argv, "b:c:fn:r")) != -1)
		switch(ch) {
		case 'b':
			ARG(512, FBYTES, RBYTES);
			break;
		case 'c':
			ARG(1, FBYTES, RBYTES);
			break;
		case 'f':
			fflag = 1;
			break;
		case 'n':
			ARG(1, FLINES, RLINES);
			break;
		case 'r':
			rflag = 1;
			break;
		case '?':
		default:
			usage();
		}
	argc -= optind;
	argv += optind;

	if (fflag && argc > 1)
		errx(1, "-f option only appropriate for a single file");

	/*
	 * If displaying in reverse, don't permit follow option, and convert
	 * style values.
	 */
	if (rflag) {
		if (fflag)
			usage();
		if (style == FBYTES)
			style = RBYTES;
		else if (style == FLINES)
			style = RLINES;
	}

	/*
	 * If style not specified, the default is the whole file for -r, and
	 * the last 10 lines if not -r.
	 */
	if (style == NOTSET) {
		if (rflag) {
			off = 0;
			style = REVERSE;
		} else {
			off = 10;
			style = RLINES;
		}
	}

	if (*argv)
		for (first = 1; (fname = *argv++);) {
			if ((fp = fopen(fname, "r")) == NULL ||
			    fstat(fileno(fp), &sb)) {
				ierr();
				continue;
			}
			if (argc > 1) {
				(void)printf("%s==> %s <==\n",
				    first ? "" : "\n", fname);
				first = 0;
				(void)fflush(stdout);
			}

			if (rflag)
				reverse(fp, style, off, &sb);
			else
				forward(fp, style, off, &sb);
			(void)fclose(fp);
		}
	else {
		fname = "stdin";
		is_stdin = 1;

		if (fstat(fileno(stdin), &sb)) {
			ierr();
			exit(1);
		}

		/*
		 * Determine if input is a pipe.  4.4BSD will set the SOCKET
		 * bit in the st_mode field for pipes.  Fix this then.
		 */
		if (lseek(fileno(stdin), (off_t)0, SEEK_CUR) == -1 &&
		    errno == ESPIPE) {
			errno = 0;
			fflag = 0;		/* POSIX.2 requires this. */
		}

		if (rflag)
			reverse(stdin, style, off, &sb);
		else
			forward(stdin, style, off, &sb);
	}
	exit(rval);
}

/*
 * Convert the obsolete argument form into something that getopt can handle.
 * This means that anything of the form [+-][0-9][0-9]*[lbc][fr] that isn't
 * the option argument for a -b, -c or -n option gets converted.
 */
static void
obsolete(char *argv[])
{
	char *ap, *p, *t;
	size_t len;
	char *start;

	while ((ap = *++argv)) {
		/* Return if "--" or not an option of any form. */
		if (ap[0] != '-') {
			if (ap[0] != '+')
				return;
		} else if (ap[1] == '-')
			return;

		switch(*++ap) {
		/* Old-style option. */
		case '0': case '1': case '2': case '3': case '4':
		case '5': case '6': case '7': case '8': case '9':

			/* Malloc space for dash, new option and argument. */
			len = strlen(*argv);
			if ((start = p = malloc(len + 4)) == NULL)
				err(1, NULL);
			*p++ = '-';

			/*
			 * Go to the end of the option argument.  Save off any
			 * trailing options (-3lf) and translate any trailing
			 * output style characters.
			 */
			t = *argv + len - 1;
			if (*t == 'f' || *t == 'r') {
				*p++ = *t;
				*t-- = '\0';
			}
			switch(*t) {
			case 'b':
				*p++ = 'b';
				*t = '\0';
				break;
			case 'c':
				*p++ = 'c';
				*t = '\0';
				break;
			case 'l':
				*t = '\0';
				/* FALLTHROUGH */
			case '0': case '1': case '2': case '3': case '4':
			case '5': case '6': case '7': case '8': case '9':
				*p++ = 'n';
				break;
			default:
				errx(1, "illegal option -- %s", *argv);
			}
			*p++ = *argv[0];
			(void)strlcpy(p, ap, start + len + 4 - p);
			*argv = start;
			continue;

		/*
		 * Options w/ arguments, skip the argument and continue
		 * with the next option.
		 */
		case 'b':
		case 'c':
		case 'n':
			if (!ap[1])
				++argv;
			/* FALLTHROUGH */
		/* Options w/o arguments, continue with the next option. */
		case 'f':
		case 'r':
			continue;

		/* Illegal option, return and let getopt handle it. */
		default:
			return;
		}
	}
}

static void
usage(void)
{
	(void)fprintf(stderr,
	    "usage: tail [-f | -r] "
	    "[-b number | -c number | -n number | -number] [file ...]\n");
	exit(1);
}