Hello-- I have solved my problem, but I don't know how. (I have kept it below for ...posterity?) What's going on here? :) When I change my sort function to the following it works as expected, sorting the dates. What is the difference between parentheses absent and parentheses present?

Working code:

sub sortByDate
{
 #get dates. will look like this: date:"2015-02-16",  date:"YYYY-MM-DD
+",
 my ($aDate) = $a =~ /date:\"(\d{4}\-\d{2}\-\d{2})"/;
 my ($bDate) = $b =~ /date:\"(\d{4}\-\d{2}\-\d{2})"/;

 return ($aDate cmp $bDate);
}
[download]

Original post:

=========

I am newish to Perl and trying to sort a file but it is behaving unexpectedly. I have a file which has several items in json format (not in date order and with some blank lines), for example:

{ date:"2015-03-01", content:"asdf" }


{ date:"2015-05-01", content:"erwa" }
{ date:"2015-01-02", content:"erts" }

{ date:"2014-04-02", content:"w34r" }
[download]

when I run my code intended to sort by date, it seems to sort the file in another way which I don't quite understand. It puts all the blank lines first, and then all the other lines stay in the order they were in the file. Here is my code:

#!/user/bin/perl
use strict;
use warnings;


# open file
open (MYFILE, '<jsonfile.json') or print ("Can't open file.");

# pull into list
my @events = <MYFILE>;

# close file
close (MYFILE);

# organize by date
sub sortByDate
{
 #get dates. will look like this: date:"2015-02-16",  date:"YYYY-MM-DD
+",
 my $aDate = $a =~ /date:\"(\d{4}\-\d{2}\-\d{2})"/;
 my $bDate = $b =~ /date:\"(\d{4}\-\d{2}\-\d{2})"/;

 return ($aDate cmp $bDate);
}

@events =  sort sortByDate @events;

&printDates;
<code>

<p>When run, I get</p>

<code>



2015-03-01
2015-05-01
2015-01-02
2014-04-02
[download]

Any help would be appreciated. I am new to custom sorts and regex.

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