How the shell script gets the random number random

The method of random number provided by C Srand and Rand, the former is to give the latter set of random number seed seeds.

int rnd_num = 0;

Srand (seed); Time (NULL) usually used to make seeds

Rnd_num = rand (); Generate random numbers

Methods of producing seeds:

1. Use Date Time

Time as a seed is very simple, take the current date and time, but there is a trap: When multiple machines concurrent execution produces random numbers, the probability of the same random number is very high. Not recommended in this way

2. Use of $random

Need system support, detected by ECHO, print out a random number to prove that the current environment supports $RANDOM, or NULL does not support:

~ @ubuntu: ~$ echo $RANDOM

2517

3. Using/dev/urandom + TR

TR-CD 0-9 </dev/urandom | Head-c 8//8-bit random seed

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Using awk to generate random numbers after the seed is taken, here is a simple function rnd2, and the arguments $ and $ are the ranges that generate random numbers, respectively.

#$1 $ is a value range
function Rnd2 () {
  If [-Z "$RANDOM"]; then
    seed= ' tr-cd 0-9 </dev/urandom | head-c 8 '
  E LSE
    seed= $RANDOM
  fi
    
  rnd_num= ' echo $SEED $ $2|awk ' {srand ($);p rintf '%d ', rand () *10000% ($3-$2) +$2} '
  echo $RND _num
}

Write a loop, loop 30 times, after the implementation of the results of the following figure:

Author: Cnblogs Lazy Man