open(LOG,"test.txt");
my $pattern = '(\s+\w+\s+\d{2}\s\d{4}) |  (Release\s+\d+\.\d+)';
while(<LOG>) {
  print $1  if($_ =~ /($pattern)/ );
}

##</code><code>##

__DATA__
December 15 2005

some line 

Flat File Release 100.0

someline