Loop between two date bash macOS and Linux

date_between.sh

#!/bin/bash

d=2020-12-01
t=2021-01-01

while [ "$d" != "$t" ]; do
  echo $d
  if [[ "$OSTYPE" == "linux-gnu"* ]]; then

     printf '=%.0s' {1..25}
     echo
     echo "Y-m-d: " $(date -d $d +"%Y-%m-%d")
     echo "  Y-m: " $(date -d $d +"%Y-%m")
     echo "    Y: " $(date -d $d +"%Y")
     echo "    m: " $(date -d $d +"%m")
     echo "    d: " $(date -d $d +"%d")
     printf '=%.0s' {1..25}
     echo
     d=$(date -I -d "$d + 1 day")

  elif [[ "$OSTYPE" == "darwin"* ]]; then

     printf '=%.0s' {1..25}
     echo
     echo "Y-m-d: " $(date -jf "%Y-%m-%d" $d +%Y-%m-%d)
     echo "  Y-m: " $(date -jf "%Y-%m-%d" $d +%Y-%m)
     echo "    Y: " $(date -jf "%Y-%m-%d" $d +%Y)
     echo "    m: " $(date -jf "%Y-%m-%d" $d +%m)
     echo "    d: " $(date -jf "%Y-%m-%d" $d +%d)
     printf '=%.0s' {1..25}
     echo
     d=$(date -j -v +1d -f "%Y-%m-%d" $d +%Y-%m-%d)
  fi

done