First, this type of thing was discussed recently in read between two strings, so maybe that will be of help.

Secondly, if people are going to be fools, then you probably have to do something besides use the range operator. A regular state system seems to work well:

my %pair = (
     'foo'   => 'bar',
     'jack'  => 'daniels',
     'Tom'   => 'Jerry',
     'BEGIN' => 'END',
);

my %data;
my $tail;
my $type;
while (<FILE>)
{
      chomp;
      s/\s+$//;    # Clean up invisible stuff

      if ($pair{$_})
      {
            $type = $_;
            $tail = $pair{$_};
      }
      elsif ($_ eq $tail)
      {
            undef $type;
      }

      push (@{$data{$type}}, "$_\n");
}
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Now you can get the stuff out of the %data hash, or deal with it some other way. YMMV.