awk 'BEGIN {
  h["0"]="0"; h["1"]="1"; h["2"]="2"; h["3"]="3"
  h["4"]="4"; h["5"]="5"; h["6"]="6"; h["7"]="7"
  h["8"]="8"; h["9"]="9"; h["A"]="10"; h["B"]="11"
  h["C"]="12"; h["D"]="13"; h["E"]="14"; h["F"]="15"
}
{
  l=length($0)
  s=h[substr($0,l--,1)]
  for(i=l;i>=1;i--) {
    s=s+ h[substr($0,i,1)]*(16^++j)
  }
  print s
}'

$ year=54
$ year=$(echo $year| awk 'BEGIN {
  h["0"]="0"; h["1"]="1"; h["2"]="2"; h["3"]="3"
  h["4"]="4"; h["5"]="5"; h["6"]="6"; h["7"]="7"
  h["8"]="8"; h["9"]="9"; h["A"]="10"; h["B"]="11"
  h["C"]="12"; h["D"]="13"; h["E"]="14"; h["F"]="15"
}
{
  l=length($0)
  s=h[substr($0,l--,1)]
  for(i=l;i>=1;i--) {
    s=s+ h[substr($0,i,1)]*(16^++j)
  }
  print s
}')
$
$ echo $year
84
$