Question

Where can I find more about the following syntax in perl?

The connection between <DATA> and __DATA__ is unclear.

while (my $date_string = <DATA>) {
  chomp($date_string);
  next if not length $date_string;
  print "$date_string ist Unixtime ",
        $lang_date->str2time($date_string),
        " und ",
    $lang_date->time2str( '%d.%m.%Y %T (%Z)',$lang_date->str2time($date_string) ),
        "\n";
}

__DATA__
1.3.1999
1 Marz 1999
1. Marz 1999
1/3/1999

Answer 1

Quoting the doc:

The __DATA__ token tells the perl compiler that the perl code for
compilation is finished.

Everything after the __DATA__ token is
available for reading via the filehandle FOOBAR::DATA, where FOOBAR is
the name of the current package when the __DATA__ token is reached.

This works just the same as __END__ does in package ‘main’, but for
other modules data after __END__ is not automatically retrievable,
whereas data after __DATA__ is.

Can add to this only that using __DATA__ section is quite handy to illustrate some file reading-related concepts in Perl. it’s basically a file attached to a code, and contents of this file are easily accessible through <DATA>. That’s why it’s quite popular here on SO. )