Bash shell script to return last four characters of base62 conversion of unix timestamp

time2base62.sh

#!/bin/bash
# takes unix timestamp and converts to base62
# source: https://stackoverflow.com/a/14472352/232251

function u2b {
  v=$(date +%s)
  BASE62=($(echo {0..9} {a..z} {A..Z}))
  for i in $(bc <<< "obase=62; $v"); do echo -n ${BASE62[$(( 10#$i ))]}
  done 
}
r=$(u2b)
echo ${r: -4}