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年03月14日 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

• craig: I was trying to combine the expressions, but failed. Thanks for the help.
• chicks: Luckily glenn can express things that most others find very challenging. :)