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#include <sys/types.h>
38#include <sys/stat.h>
39
40#include <err.h>
41#include <stdio.h>
42#include <stdlib.h>
43#include <string.h>
44#include <unistd.h>
45
46static void usage(void) __dead2;
47
48int
49main(int argc, char *argv[])
50{
51	struct stat sb;
52	char *tty;
53	int ch;
54
55	while ((ch = getopt(argc, argv, "")) != -1)
56		switch (ch) {
57		case '?':
58		default:
59			usage();
60		}
61	argc -= optind;
62	argv += optind;
63
64	if ((tty = ttyname(STDIN_FILENO)) == NULL &&
65	    (tty = ttyname(STDOUT_FILENO)) == NULL &&
66	    (tty = ttyname(STDERR_FILENO)) == NULL)
67		err(2, "ttyname");
68	if (stat(tty, &sb) < 0)
69		err(2, "%s", tty);
70
71	if (*argv == NULL) {
72		if (sb.st_mode & S_IWGRP) {
73			(void)puts("is y");
74			exit(0);
75		}
76		(void)puts("is n");
77		exit(1);
78	}
79
80	switch (*argv[0]) {
81	case 'y':
82		if (chmod(tty, sb.st_mode | S_IWGRP) < 0)
83			err(2, "%s", tty);
84		exit(0);
85	case 'n':
86		if (chmod(tty, sb.st_mode & ~S_IWGRP) < 0)
87			err(2, "%s", tty);
88		exit(1);
89	}
90
91	usage();
92	return(0);
93}
94
95static void
96usage(void)
97{
98	(void)fprintf(stderr, "usage: mesg [n | y]\n");
99	exit(2);
100}
101