Need help figuring out why below program wont run

Write a PERL program that opens and reads the calendar file. Then the program writes back in the calendar file the original content, sorted in ascending order by date.

The main code should be 7 lines of code, or less:

open the file for input

read all the input data

close the file

sort the dates

open the file for output

print the result to the file

close the file

Use the sort function. In addition to the main code, you will need to code a sort subroutine that compares the dates of two records. This subroutine should be called by the sort function.

I have the below codeso far, but i am getting the error - Use of uninitialized value in numeric comparison (<=>) at probleme3.pl line 28.

open (my $fh, "<", "calender.txt") or die "Can't open file!"; # here we open the file called calender

push(@events, $_) while(<$fh>);

close($fh);

my @sortedevents = sort dateSort @events;

open(my $oh, ">", "sortedCalendar");

print $oh @sortedevents;

close($oh);

# dateSort returns whether a date is before another date

sub dateSort{

$a =~ /(\d{1,2})\/(\d{1,2})\/(\d{4})/;

$a =~ /(\d{1,2})\/(\d{1,2})\/(\d{4})/;

$b =~ /(\d{1,2})\/(\d{1,2})\/(\d{4})/;

my @date2 = ($1, $2, $3);

$date1[2] <=> $date2[2] || $date1[0] <=> $date2[0] || $date1[1] <=> $date2[1];

}

CALENDER.txt

11/17/1999 - Doctor's appointment.

12/6/1999 - Dentist appointment.

12/23/1999 - Christmas party.

1/23/2000 - Meet with business advisor.

1/13/2000 - Business trip to Hong Kong.

2/25/2000 - Business trip to Kansas City.

1/5/2000 - Car service.

3/18/2000 - Birthday party.

4/10/2000 - Meet with tax accountant.

3/12/2000 - Conference in San Jose.

12/31/1999 - New Year's party.