2008-10-01 message 1
2008-10-02 message 2
2008-10-03 multi-line message
         message 3 keyword
2008-10-04 message 4
2008-10-05 multi-line
         blah blah
         message 5 keyword junk
2008-10-06 message 6 blah keyword
2008-10-06 this is message 7

##</code><code>##

2008-10-03 multi-line message
         message 3 keyword
2008-10-05 multi-line
         blah blah
         message 5 keyword junk
2008-10-06 message 6 blah keyword

##</code><code>##

undef $/;
while ( /^(\d+-\d+-\d+.*?keyword)(?!\d+-\d+)$/smg ) {
      print "$1\n";
}