サンプルCSVファイルからデータを生成する

cat 6months.pl 

#!/usr/bin/env perl
use Text::CSV;
use DateTime;
use DateTime::Format::Strptime;
use autodie     qw/ open close /;

my $csv = Text::CSV->new({binary => 1, quote_space => 0}); 
my $dateparser = DateTime::Format::Strptime->new(pattern => "%d/%m/%Y %T", time_zone => "local");

for my $file (@ARGV) {
    open my $fh, '<', $file;
    while (my $row = $csv->getline($fh)) {
        my $datestr = shift @$row;
        my $date = $dateparser->parse_datetime($datestr)->truncate(to => month);
        my $end = $date->clone->add(months => 6);
        while ($date <= $end) {
            $csv->say(STDOUT, [$dateparser->format_datetime($date), @$row]);
            $date = $date->add(days => 1);
        }
    }
    close $fh;
}

実行してください：

perl 6months.pl data.csv 

01/01/2017 00:00:00,sampledata,1234,sample,123455,67546464
02/01/2017 00:00:00,sampledata,1234,sample,123455,67546464
...
30/06/2017 00:00:00,sampledata,1234,sample,123455,67546464
01/07/2017 00:00:00,sampledata,1234,sample,123455,67546464

---

これで時間が真夜中にリセットされることがわかりました。時間を節約するには:

    my $date = $dateparser->parse_datetime($datestr)->set(day => 1);
    #                                                 ^^^^^^^^^^^^^