Random

Basic

Use the RANDOM variable to generate a random number.

$ echo $RANDOM
31267

Range

Use the modulus operator to get a number between 0 and N - 1.

$ $RANDOM % 3

That will generate a value as 0, 1, or 2.

Control flow

Use a condition agains the value. Here if the value is 0 (with a 1 in 3 chance), then the script will exit with a success. Note use of double brackets for maths evaluations to handle %.

(( $RANDOM % 3 != 0 )) && (echo 'Skipping' ; exit 0)

# Do stuff

if (( $RANDOM % 3 != 0 )) ; then
  echo 'Condition matched'
else
  echo 'Not matched'
fi