Parse a selection of date formats

Question

This Bash program parses day, month, year and month and year from arguments:

#!/usr/bin/env bash

for arg
do
    day= month= year=
    case $arg in

    */*/*|*-*-*)
        read -r year month day <<< "$(date '+%Y %m %d' -d "$arg")"
        ;;

    ????/??|????/?)
        IFS='/' read -r -a arr <<< "$arg"
        month=${arr[1]} year=${arr[0]}
        ;;

    ????-??|????-?)
        IFS='-' read -r -a arr <<< "$arg"
        month=${arr[1]} year=${arr[0]}
        ;;

    ??/????|?/????)
        IFS='/' read -r -a arr <<< "$arg"
        month=${arr[0]} year=${arr[1]}
        ;;

    ??-????|?-????)
        IFS='-' read -r -a arr <<< "$arg"
        month=${arr[0]} year=${arr[1]}
        ;;

    esac

    echo "year: $year / month: $month / day: $day"

done

Usage:

./parse.sh 2021-03 2021-03-14 3/14/19 11/2019 2020/12
year: 2021 / month: 03 / day: 
year: 2021 / month: 03 / day: 14
year: 2019 / month: 03 / day: 14
year: 2019 / month: 11 / day: 
year: 2020 / month: 12 / day: 

It seems overly-verbose to me. Can I write it more succinctly?

Answer 1

How about

for arg do
    day= month= year=

    case $arg in
      */*/* | *-*-*)
          read -r year month day < <(date '+%Y %m %d' -d "$arg")
          ;;
      ????[-/]?? | ????[-/]?)
          IFS='-/' read -r year month <<< "$arg"
          ;;
      ??[-/]???? | ?[-/]????)
          IFS='-/' read -r month year <<< "$arg"
          ;;
    esac

    echo "year: $year / month: $month / day: $day"
done

• remove pointless read into array
• IFS can be more than one character