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Bash function $RANDOM

To generate a random integer we can use the internal bash function $RANDOM.
This functions returns integer between 0 and 32767.

Example:

[www1.linuxnix] root:~ # i=$RANDOM
[www1.linuxnix] root:~ # echo $i
23770
[www1.linuxnix] root:~ # j=$RANDOM
[www1.linuxnix] root:~ # echo $j
3577

To generate a random integer between 1 and 1000, you can use $RANDOM like below:

$(((RANDOM%1000+1)))

Note : $(((RANDOM%1000))) will generate integer between 0 and 999.

Examples:

[www1.linuxnix] root:~ # i=$(((RANDOM%1000+1)))
[www1.linuxnix] root:~ # echo $i
895
[www1.linuxnix] root:~ # j=$(((RANDOM%1000+1)))
[www1.linuxnix] root:~ # echo $j
316

 

/dev/random and /dev/urandom

For bigger integer random generation we can use /dev/random and /dev/urandom which can interact with kernel’s random number generator. We will use the od command for that :

od : dump files in octal and other formats

we will use arguments :
-A or –address-radix=RADIX : output format for file offsets; RADIX is one of [doxn], for Decimal, Octal, Hex or None
-N or –read-bytes=BYTES : limit dump to BYTES input bytes
-t or –format=TYPE : select output format or formats

[www1.linuxnix] root:~ # od  -An -N8 -tu8 < /dev/urandom
 11055529178234849100
[www1.linuxnix] root:~ # od -An -N4 -tu4 < /dev/random
 3202521020

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ZIADI Mohamed Ali

I am a hands-on, competent Linux system engineer with 9 years’ experience. I have a strong performance background in wide variety of professional Linux system support including monitoring, configuration, troubleshooting and maintenance. I have worked on numerous projects from concept to completion. A specialist in LAMP platforms, I take pride in administrating Linux systems and regularly refresh my skills to ensure I keep up with ongoing developments and new technologies.