use strict;
my $str = '
2020-01-01
2020-01-31
2020-02-29
2020-03-31
2020-04-30
2020-05-31
2020-06-30
2020-07-31
2020-08-31
2020-09-30
2020-10-31
2020-11-30
2020-12-31
2020-01-01 00:00:00,000
2020-01-01_00:00:00,000
2020-01-01-00:00:00,000
2020-01-01T00:00:00,000
2222-01-01
2222/11/22
2222.11.22
// Invalid dates
2020-00-01
2020-01-00
000-01-01
222-01-01
2020-1-1
2020-1-01
2020-01-1
2020-22-01
2020-01-33
2020-01-32
2020-02-30
2020-03-32
2020-04-31
2020-05-32
2020-06-31
2020-07-32
2020-08-32
2020-09-31
2020-10-32
2020-11-31
2020-12-32
a222-01-01
2a22-01-01
22a2-01-01
222a-01-01
2222-a1-01
2222-0a-01
2222-1a-01
2222-01-a1
2222-01-0a
2222-01-1a';
my $regex = qr/(?<=\D|^)(?<year>\d{4})(?<sep>[^\w\s])(?<month>1[0-2]|0[1-9])\k<sep>(?<day>0[1-9]|[12][0-9]|(?<=11\k<sep>|[^1][4-9]\k<sep>)30|(?<=1[02]\k<sep>|[^1][13578]\k<sep>)3[01])(?=\D|$)/mp;
if ( $str =~ /$regex/g ) {
print "Whole match is ${^MATCH} and its start/end positions can be obtained via \$-[0] and \$+[0]\n";
# print "Capture Group 1 is $1 and its start/end positions can be obtained via \$-[1] and \$+[1]\n";
# print "Capture Group 2 is $2 ... and so on\n";
}
# ${^POSTMATCH} and ${^PREMATCH} are also available with the use of '/p'
# Named capture groups can be called via $+{name}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html