The match operator is not particularly well suited to extract this data since the data has two dimensions. One solution: 
while (
   /
      ^
      (\d{4}-\d\d-\d\d)
      .*dates processed:[ ]
      ( (?:\d{4}-\d\d-\d\d,[ ])* \d{4}-\d\d-\d\d )
      $
   /mg
) {
   my $on        = $1;
   my $procesed  = $2;
   my @processed = split(/, /, $processed);

   # Do something with $on and @processed.
}

[download]

Or if you are dealing with a file handle, 

while (<$fh>) {
   my ($on, $processed) = /
      ^
      (\d{4}-\d\d-\d\d)
      .*dates processed:[ ]
      ( (?:\d{4}-\d\d-\d\d,[ ])* \d{4}-\d\d-\d\d )
      $
   /
      or next;

   my @processed = split(/, /, $processed);

   # Do something with $on and @processed.
}

[download]

Update: Added file handle version since that's probably what the OP really wants.

In reply to Re: regex: extract multiple number of date patterns from certain lines by ikegami
in thread regex: extract multiple number of date patterns from certain lines by Random_Walk

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