11-14-2002
Suppose that you want to pick a random line froma file that has exactly 100 lines. You can label the lines 0 through 99. Then if you get a random integer, you just take the last two digits as your line number.
Those last 2 digits are the remainder that your get when you divide the random integer by 100. So for example, if the random integer is 10726352; you would have a remainder of 52 after dividing 10726352 by 100. This is expressed as
10726352 % 100 = 52
and % is sometimes called "the remainder function". And sometimes "modulus".
But is was important to divide by 100 since we had 100 lines in our file. When we divide by 100, we have 100 possible remainders, so each line in the file has a chance.
To make this general, don't divide by 100 (or 50) all the time, divide by the count of items.
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LEARN ABOUT DEBIAN
bup-random
bup-random(1) General Commands Manual bup-random(1)
NAME
bup-random - generate a stream of random output
SYNOPSIS
bup random [-S seed] [-fv]
DESCRIPTION
bup random produces a stream of pseudorandom output bytes to stdout. Note: the bytes are not generated using a cryptographic algorithm and
should never be used for security.
Note that the stream of random bytes will be identical every time bup random is run, unless you provide a different seed value. This is
intentional: the purpose of this program is to be able to run repeatable tests on large amounts of data, so we want identical data every
time.
bup random generates about 240 megabytes per second on a modern test system (Intel Core2), which is faster than you could achieve by read-
ing data from most disks. Thus, it can be helpful when running microbenchmarks.
OPTIONS
the number of bytes of data to generate.
Can be used with the suffices k, M, or G to indicate kilobytes, megabytes, or gigabytes, respectively.
-S, --seed=seed
use the given value to seed the pseudorandom number generator. The generated output stream will be identical for every stream
seeded with the same value. The default seed is 1. A seed value of 0 is equivalent to 1.
-f, --force
generate output even if stdout is a tty. (Generating random data to a tty is generally considered ill-advised, but you can do if
you really want.)
-v, --verbose
print a progress message showing the number of bytes that has been output so far.
EXAMPLES
$ bup random 1k | sha1sum
2108c55d0a2687c8dacf9192677c58437a55db71 -
$ bup random -S1 1k | sha1sum
2108c55d0a2687c8dacf9192677c58437a55db71 -
$ bup random -S2 1k | sha1sum
f71acb90e135d98dad7efc136e8d2cc30573e71a -
$ time bup random 1G >/dev/null
Random: 1024 Mbytes, done.
real 0m4.261s
user 0m4.048s
sys 0m0.172s
$ bup random 1G | bup split -t --bench
Random: 1024 Mbytes, done.
bup: 1048576.00kbytes in 18.59 secs = 56417.78 kbytes/sec
1092599b9c7b2909652ef1e6edac0796bfbfc573
BUP
Part of the bup(1) suite.
AUTHORS
Avery Pennarun <apenwarr@gmail.com>.
Bup unknown- bup-random(1)