TIL - Unix shells have a $RANDOM env variable

Ever wanted to add some randomness to your shell script? No I don't mean to make them flaky!

Unix shells provide a $RANDOM environment variable that we can use in our shell commands or scripts:

% echo $RANDOM 
21290
% echo $RANDOM
8367

The seed for the random number generator can be changed as follows:

% RANDOM=12345
% echo $RANDOM
5758

Generating random numbers in a range

We can use awk for generating random integers in a given range. For example, to generate a random number between 1 and 10 (inclusive):

% awk -v seed=$RANDOM 'BEGIN{srand(seed); print int(rand()*10+1)}'
10
% awk -v seed=$RANDOM 'BEGIN{srand(seed); print int(rand()*10+1)}'
4
% awk -v seed=$RANDOM 'BEGIN{srand(seed); print int(rand()*10+1)}'
1

More details at:

• http://srufaculty.sru.edu/david.dailey/unix/random_numbers.htm

Comments

[Meghan (she/her)]

Note: this value is generated on the fly and not available in all evironments

[Parambir Singh]

Yes, you are right. I'm using fish shell these days and it doesn't have this feature.