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random.c revision 1.2 
      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
     38 static 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
     44 static 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 #include <limits.h>
     56 
     57 void usage __P((void));
     58 
     59 int
     60 main(argc, argv)
     61 	int argc;
     62 	char *argv[];
     63 {
     64 	extern int optind;
     65 	time_t now;
     66 	double denom;
     67 	int ch, random_exit, selected, unbuffer_output;
     68 	char *ep;
     69 
     70 	random_exit = unbuffer_output = 0;
     71 	while ((ch = getopt(argc, argv, "er")) != EOF)
     72 		switch (ch) {
     73 		case 'e':
     74 			random_exit = 1;
     75 			break;
     76 		case 'r':
     77 			unbuffer_output = 1;
     78 			break;
     79 		default:
     80 		case '?':
     81 			usage();
     82 			/* NOTREACHED */
     83 		}
     84 
     85 	argc -= optind;
     86 	argv += optind;
     87 
     88 	switch (argc) {
     89 	case 0:
     90 		denom = 2;
     91 		break;
     92 	case 1:
     93 		errno = 0;
     94 		denom = strtod(*argv, &ep);
     95 		if (errno == ERANGE)
     96 			err(1, "%s", *argv);
     97 		if (denom == 0 || *ep != '\0')
     98 			errx(1, "denominator is not valid.");
     99 		break;
    100 	default:
    101 		usage();
    102 		/* NOTREACHED */
    103 	}
    104 
    105 	(void)time(&now);
    106 	srandom((u_int)(now + getpid()));
    107 
    108 	/* Compute a random exit status between 0 and denom - 1. */
    109 	if (random_exit)
    110 		return ((denom * random()) / LONG_MAX);
    111 
    112 	/*
    113 	 * Act as a filter, randomly choosing lines of the standard input
    114 	 * to write to the standard output.
    115 	 */
    116 	if (unbuffer_output)
    117 		setbuf(stdout, NULL);
    118 
    119 	/*
    120 	 * Select whether to print the first line.  (Prime the pump.)
    121 	 * We find a random number between 0 and denom - 1 and, if it's
    122 	 * 0 (which has a 1 / denom chance of being true), we select the
    123 	 * line.
    124 	 */
    125 	selected = (int)(denom * random() / LONG_MAX) == 0;
    126 	while ((ch = getchar()) != EOF) {
    127 		if (selected)
    128 			(void)putchar(ch);
    129 		if (ch == '\n') {
    130 			/* End of that line.  See if we got an error. */
    131 			if (ferror(stdout))
    132 				err(2, "stdout");
    133 
    134 			/* Now see if the next line is to be printed. */
    135 			selected = (int)(denom * random() / LONG_MAX) == 0;
    136 		}
    137 	}
    138 	if (ferror(stdin))
    139 		err(2, "stdin");
    140 	exit (0);
    141 }
    142 
    143 void
    144 usage()
    145 {
    146 
    147 	(void)fprintf(stderr, "usage: random [-er] [denominator]\n");
    148 	exit(1);
    149 }
    150