How the shell generates a specified range of random numbers and random strings

1. Use the system $RANDOM variables

fdipzone@ubuntu:~$ Echo $RANDOM  
17617

The range of the $RANDOM is [0, 32767]

If you need to generate more than 32767 random numbers, you can do so in the following ways.

Example: Generating random numbers of 400000~500000

#!/bin/bash  
      
function rand () {  
    min=$1  
    max=$ ($2-$min + 1))  
    num=$ (($RANDOM +1000000000)) #增加一个10位的数再求余  
    echo $ ($num% $max + $min)  
}  
      
rnd=$ (Rand 400000 500000)  
echo $rnd  
      
exit 0

2. Use Date +%s%n

Example: Generating random numbers of 1~50

#!/bin/bash  
      
function rand () {  
    min=$1  
    max=$ ($2-$min + 1))  
    num=$ (date +%s%n)  
    echo $ ($num%$ max+ $min))  
}  
      
rnd=$ (rand 1)  
echo $rnd  
      
exit 0

3. Use of/dev/random and/dev/urandom

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/dev/random stores the real-time data of the system's current operating environment, which is a blocking random number generator and sometimes needs to wait for reading.

/dev/urandom non-blocking random number generator, the read operation does not cause blocking.

Example: Using/dev/urandom to generate 100~500 random numbers, use urandom to avoid blocking.

#!/bin/bash  
      
function rand () {  
    min=$1  
    max=$ ($2-$min + 1))  
    num=$ (cat/dev/urandom | head-n | cksum | awk -F ' ' {print} ')  
    echo $ (($num% $max + $min))  
}  
      
rnd=$ (rand)  
echo $rnd  
      
exit 0

4. Using the Linux UUID

The UUID full name is a universal unique identifier that contains 32 16 digits, and the '-' connection number is divided into 5 segments. 32 characters in the form of 8-4-4-4-12.

fdipzone@ubuntu:~/shell$ Cat/proc/sys/kernel/random/uuid  
FD496199-372A-403E-8EC9-BF4C52CBD9CD

Example: generating 100~500 random numbers using a Linux UUID

#!/bin/bash  
      
function rand () {  
    min=$1  
    max=$ ($2-$min + 1))  
    num=$ (cat/proc/sys/kernel/random/ UUID | Cksum | Awk-f ' {print} ')  
    echo $ (($num% $max + $min))  
}  
      
rnd=$ (rand)  
echo $rnd  
      
exit 0

5. Generate Random strings

Example: generating 10-bit random strings

#use date generate a random string  
date +%s%n | md5sum | head-c  
      
#use /dev/urandom Generate random string  
cat/dev/urandom | head-n | md5s Um | Head-c 10