Get Last Character of Variable

main() {
  HI="12"
  last_char="${HI: -1}"
 
  echo "last_char='${last_char}'"
}
 
main "${@}" || exit 1
 

main() {
  last_char="${HI_I_DONT_EXIST: -1}"
 
  echo "last_char='${last_char}'"
}
 
main "${@}" || exit 1