Get dates for Nth weekday in month: eg. get every 3rd tuesday of next 12 months

weekday_in_month.sh

#!/bin/bash

if [ $# -lt 2 ]
then
    echo "Usage: $0 <day_in_week> <week_in_month> [<nb_months>]"
    echo "    day_in_week: [0-6] (Sun=0 Mon=1 Tue=2 Wed=3 Thu=4 Fri=5 Sat=6)"
    echo "    week_in_month: [1-5]"
fi

day_in_week=$1
week_in_month=$2
nb_months=${3:-12}
nb_days=$(($nb_months * 31))

d0=$(date +"%Y%m01")
_m=""

i=0
while [ $i -le $nb_days ]
do
    read -r w m d < <(date -d"$d0 $i day" +"%w %m %d/%m/%Y")
    if [ "$m" != "$_m" ]
    then
        _m="$m"
        _cnt=0
    fi
    if [ "$w" == "$day_in_week" ]
    then
        _cnt=$(($_cnt + 1))
        if [ "$_cnt" == "$week_in_month" ]
        then
            echo $d
        fi
        i=$(($i + 7))
    else
        i=$(($i + 1))
    fi
done