Find time gaps in job logs

# Find time gaps in a joblog, sorting by time differences between successive records
# Entries of the Job Log are of the form
#
# |15.12.2020|04:07:17|Datei ATRON_STAMMDATEN.CSV enthält 720 Fehler; folgende "Arten" (Alle=ZAFM_LIEF_STAT1): | ZAFM | 156 | S |
# |15.12.2020|04:07:17|720 Fehler mit ZAFM-011: Doppelter GTIN & bei Lieferant & Zeilennummer &.               | ZAFM | 157 | S |
# |15.12.2020|04:47:22|Insgesamt wurden 158757 Zeilen abgespeichert aus Datei ATRON_STAMMDATEN.CSV.            | ZAFM | 009 | S |
#
# Log lines which don't start with date and time like these are ignored

use DateTime;

use constant {
# Constant filename:
# Use fixed filename, or $ARGV[0] from the command line
  JOBLOG_FILENAME    => $ARGV[0] || "C:\\Temp\\joblog.txt",
# Show only the top 20 time gap entries:
  TOP                => $ARGV[1] || 20,
# Change the regex DATE_TIME_PATTERN to catch the date and time for different log formats:
  DATE_TIME_PATTERN  => qr/^\|(\d{2})\.(\d{2})\.(\d{4})\|(\d{2}):(\d{2}):(\d{2})/
};

open JOBLOG, "<", JOBLOG_FILENAME or die "Can't open ${ \JOBLOG_FILENAME }: $!\n";

my @log = ();
my $last_time = 0;
foreach my $line ( <JOBLOG> ) {
  next unless my @dt = ( $line =~ DATE_TIME_PATTERN );
  my $this_time = new DateTime(
    day    => $dt[0],
    month  => $dt[1],
    year   => $dt[2],
    hour   => $dt[3],
    minute => $dt[4],
    second => $dt[5]
  );
  if ($last_time) {
    push @log, [ $this_time->epoch - $last_time->epoch, $line ];
  }
  $last_time = $this_time;
}

# In Perl, "@a = sort @a" sorts @a inplace internally (no copying):
@log = sort { $b->[0] <=> $a->[0] } @log;

foreach $a (@log[0..TOP-1]) {
  printf( "%5d %s", $a->[0], $a->[1] );
}

close JOBLOG;