On some light linux environement running busybox or openWRT you will notice that you don’t have access to the $RANDOM variable ,
the date command is also incomplete so you can’t use the tail of the nanosecond date to have a random number.

grep -m1 -ao '[0-6][0-9]' /dev/urandom | head -n1

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Using this command you will get a random number beetween 0 and 69.
if you wish to change the range of the random numbers , just edit the regex in the grep part