mesg.c revision 330897 
1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1987, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 * (c) UNIX System Laboratories, Inc.
7 * All or some portions of this file are derived from material licensed
8 * to the University of California by American Telephone and Telegraph
9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
10 * the permission of UNIX System Laboratories, Inc.
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 *    notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 *    notice, this list of conditions and the following disclaimer in the
19 *    documentation and/or other materials provided with the distribution.
20 * 3. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#ifndef lint
38static const char copyright[] =
39"@(#) Copyright (c) 1987, 1993\n\
40	The Regents of the University of California.  All rights reserved.\n";
41#endif /* not lint */
42
43#ifndef lint
44#if 0
45static char sccsid[] = "@(#)mesg.c	8.2 (Berkeley) 1/21/94";
46#endif
47#endif /* not lint */
48#include <sys/cdefs.h>
49__FBSDID("$FreeBSD: stable/11/usr.bin/mesg/mesg.c 330897 2018-03-14 03:19:51Z eadler $");
50
51#include <sys/types.h>
52#include <sys/stat.h>
53
54#include <err.h>
55#include <stdio.h>
56#include <stdlib.h>
57#include <string.h>
58#include <unistd.h>
59
60static void usage(void);
61
62int
63main(int argc, char *argv[])
64{
65	struct stat sb;
66	char *tty;
67	int ch;
68
69	while ((ch = getopt(argc, argv, "")) != -1)
70		switch (ch) {
71		case '?':
72		default:
73			usage();
74		}
75	argc -= optind;
76	argv += optind;
77
78	if ((tty = ttyname(STDIN_FILENO)) == NULL &&
79	    (tty = ttyname(STDOUT_FILENO)) == NULL &&
80	    (tty = ttyname(STDERR_FILENO)) == NULL)
81		err(2, "ttyname");
82	if (stat(tty, &sb) < 0)
83		err(2, "%s", tty);
84
85	if (*argv == NULL) {
86		if (sb.st_mode & S_IWGRP) {
87			(void)puts("is y");
88			exit(0);
89		}
90		(void)puts("is n");
91		exit(1);
92	}
93
94	switch (*argv[0]) {
95	case 'y':
96		if (chmod(tty, sb.st_mode | S_IWGRP) < 0)
97			err(2, "%s", tty);
98		exit(0);
99	case 'n':
100		if (chmod(tty, sb.st_mode & ~S_IWGRP) < 0)
101			err(2, "%s", tty);
102		exit(1);
103	}
104
105	usage();
106	return(0);
107}
108
109static void
110usage(void)
111{
112	(void)fprintf(stderr, "usage: mesg [n | y]\n");
113	exit(2);
114}
115