random.c revision 2490 
1/*
2 * Copyright (c) 1994
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Guy Harris at Network Appliance Corp.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. 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 char copyright[] =
39"@(#) Copyright (c) 1994\n\
40	The Regents of the University of California.  All rights reserved.\n";
41#endif /* not lint */
42
43#ifndef lint
44static char sccsid[] = "@(#)random.c	8.5 (Berkeley) 4/5/94";
45#endif /* not lint */
46
47#include <sys/types.h>
48
49#include <err.h>
50#include <errno.h>
51#include <stdio.h>
52#include <stdlib.h>
53#include <time.h>
54#include <unistd.h>
55
56void usage __P((void));
57
58int
59main(argc, argv)
60	int argc;
61	char *argv[];
62{
63	extern int optind;
64	time_t now;
65	double denom;
66	int ch, random_exit, selected, unbuffer_output;
67	char *ep;
68
69	random_exit = unbuffer_output = 0;
70	while ((ch = getopt(argc, argv, "er")) != EOF)
71		switch (ch) {
72		case 'e':
73			random_exit = 1;
74			break;
75		case 'r':
76			unbuffer_output = 1;
77			break;
78		default:
79		case '?':
80			usage();
81			/* NOTREACHED */
82		}
83
84	argc -= optind;
85	argv += optind;
86
87	switch (argc) {
88	case 0:
89		denom = 2;
90		break;
91	case 1:
92		errno = 0;
93		denom = strtod(*argv, &ep);
94		if (errno == ERANGE)
95			err(1, "%s", *argv);
96		if (denom == 0 || *ep != '\0')
97			errx(1, "denominator is not valid.");
98		break;
99	default:
100		usage();
101		/* NOTREACHED */
102	}
103
104	(void)time(&now);
105	srandom((u_int)(now + getpid()));
106
107	/* Compute a random exit status between 0 and denom - 1. */
108	if (random_exit)
109		return ((denom * random()) / LONG_MAX);
110
111	/*
112	 * Act as a filter, randomly choosing lines of the standard input
113	 * to write to the standard output.
114	 */
115	if (unbuffer_output)
116		setbuf(stdout, NULL);
117
118	/*
119	 * Select whether to print the first line.  (Prime the pump.)
120	 * We find a random number between 0 and denom - 1 and, if it's
121	 * 0 (which has a 1 / denom chance of being true), we select the
122	 * line.
123	 */
124	selected = (int)(denom * random() / LONG_MAX) == 0;
125	while ((ch = getchar()) != EOF) {
126		if (selected)
127			(void)putchar(ch);
128		if (ch == '\n') {
129			/* End of that line.  See if we got an error. */
130			if (ferror(stdout))
131				err(2, "stdout");
132
133			/* Now see if the next line is to be printed. */
134			selected = (int)(denom * random() / LONG_MAX) == 0;
135		}
136	}
137	if (ferror(stdin))
138		err(2, "stdin");
139	exit (0);
140}
141
142void
143usage()
144{
145
146	(void)fprintf(stderr, "usage: random [-er] [denominator]\n");
147	exit(1);
148}
149