#!/bin/bash
day_of_month=$(date +"%d")
day_of_month=$(echo $day_of_month | sed 's/^0*//')
if [[ $day_of_month -ge 11 && $day_of_month -le 13 ]]; then
    suffix="th"
else
    case $((day_of_month % 10)) in
        1) suffix="ST" ;;
        2) suffix="ND" ;;
        3) suffix="RD" ;;
        *) suffix="TH" ;;
    esac
fi
echo "${day_of_month}${suffix}"