In a regular expression you can capture strings into variables using the default syntax:

$str = "2020-05-20";
$str =~ m/(\d{4})-(\d{2})-(\d{2})/;

printf("Year: %s Month: %s Day: %s\n", $1, $2, $3);

In a more complex regular expression/string things may move around. In this case it's better to use named captures instead of numeric captures. This can be done by using the (?<name>) syntax. This will capture that parenthesis pair in to the hash %+ with the name specified.

$str = "2020-05-20";
$str =~ m/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/;

printf("Year: %s Month: %s Day: %s\n", $+{year},$+{month},$+{day});

Using named captures you can easily update your regular expression if the position of elements in your string change.

Note: If you use named captures, Perl also populates the numeric equivalent.