In scalar context, the match operator and thus the bind operator returns whether a match was found or not. You want to evaluate the match in list context to get it to return the list of matches.

Fix:

   my ($aDate) = $a =~ /\bdate:\s*"(\d{4}-\d{2}-\d{2})"/;
   my ($bDate) = $b =~ /\bdate:\s*"(\d{4}-\d{2}-\d{2})"/;
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Also:

• Added \b to avoid catching enddate.
• Added \s* in case the JSON encoder decides to start adding whitespace.
• Removed some superfluous backslashes.

Note: Will break if you get

• { date:"\u0032015-05-01", content:"erwa" }
• { foo:{date:"2014-05-01"}, date:"2015-05-01", content:"erwa" }
• etc

For a reliable but slower solution, you can use

use JSON::XS qw( decode_json );

my @sorted =
   map { substr($_, 10) }
      sort
         map { decode_json($_)->{date} . $_ }
            @events;
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As for the blank lines, just remove them first using

@events = grep /\S/, @events;
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Update: Added to my answer.