#!/bin/bash

now=`/bin/date +%s`
onemonth="2592000"
validperiods="1 3 6 12"
for period in $validperiods
do
  epochs[$period]=`expr $now - \( $period \* $onemonth \)`
done

for i in "${epochs[@]}"
do
  echo "i: ${i}"
  echo "key: " # i need to know if it's 1, 3, 6 or 12
  echo "value: ${epochs[$i]}" # this does not seem to work
  echo "--"
done