Creating a custom random variable

Question

I want to create a custom variable or command that can be called on like $RANDOM, but for strings. I have a script that creates a random string, using /dev/urandom . The script produces a randomly generated string each time the script is run.

#!/bin/bash

rando=$(head -100 /dev/urandom | tr -dc a-zA-Z0-9 | fold -w 15 | head -1)

echo $rando

If I create an alias or environmental variable that calls on the script, it will produce only one variation of a random string until a new bash sessions is created. How can I make it so it will create a new variation of the random string in the same bash session?

Wrap it up in a function in your .bashrc. Then every time you call it, the code will run. — JNevill
– JNevill, Commented Nov 25, 2019 at 19:13
Huh? The variable $rando is of course the same until you change it, but calling dd etc again will create a new value each time. Or are you asking how to make a function around this code? — tripleee
– tripleee, Commented Nov 25, 2019 at 19:15
RANDOM is a special built-in parameter; you can't define your own variable whose value changes every time you expand it. — chepner
– chepner, Commented Nov 25, 2019 at 20:05
This might work, too: tr -dc a-zA-Z0-9 </dev/urandom | head -c 15 — Cyrus
– Cyrus, Commented Nov 25, 2019 at 20:08
Worked like a charm @JNevill . This accomplished what I wanted to do. Thank you — Ryan St Louis
– Ryan St Louis, Commented Nov 25, 2019 at 20:23

Matias Barrios · Accepted Answer · 2019-11-25 19:18:04Z

2

As replied by JNevill, you can place it as a function in your bash profile :

function RANDOM(){
    rando=$( head -100 /dev/urandom | tr -dc a-zA-Z0-9 | fold -w ${1:-15} | head -1 )
    echo $rando
}

RANDOM
RANDOM 4
RANDOM 40

Output

17oxDRkl2O1c9iz
vfgZ
4xlVNyINrBj8XT04nkQWIVOTHAV51eVxtVNEyRW0

I added an optional first argument so you can control the length of the string as well.

answered Nov 25, 2019 at 19:18

Matias Barrios

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4 Comments

Ryan St Louis Over a year ago

This is exactly what I was looking to accomplish, thank you! So this works because it calls on the function each time to create the string, rather than a variable being declared by the script when bash starts up, right? Why does an alias that calls on the script not work then?

Matias Barrios Over a year ago

Im not sure of your actual implementation. But for what you describe, you seem to be confusing environment variables with aliases. if you do this : export RANDOM=$(SOME COMMAND CALL HERE) the value of RANDOM will always be the same. While if you create an alias you always get an actual command being executed. Anyway, I almost always end up using functions instead of aliases. Code can be more complex and easier to read. So if in doubt, I would recommend to default to functions most of the time and avoid aliasing.

Ryan St Louis Over a year ago

Starting to use functions more in my scripts, as they do make everything look a lot cleaner. Thank you for your insight, marked your answer as the solution. :)

Gordon Davisson Over a year ago

I'd recommend simplifying this by removing the rando variable and echo -- just have the pipeline produce output directly.

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