If your file consists of blocks separated by (say) 60 *'s, you could do this:

$/ = '*' x 60 . "\n";
while (my $block = <>) {
  # Do something to $block...
  print $block;
}
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On every iteration, $block will consist of all lines until the next line "******...\n" (including that line).

Just remember, every block contains multiple lines! This is important if using s/.../.../ in your processing.

See perlvar for more information about the wondrous $/ variable.

Originally posted as a Categorized Answer.