Rather than write a daemon, just remember the seek position of the end of the last line you processed. Store this somewhere sensible and then start from there. Something like (untested, no error checking, yadda yadda)

$log = "foo.log";
$pos_file = $log . ".pos";
$pos = 0;
if( open POS, "<$pos_file" ) {
  $pos = <POS>;
  close POS;
}
open FILE, $log;
seek FILE, $pos, 0;
...process file until eof...
$pos = tell FILE;
open POS, ">$pos_file";
print POS $pos;
close POS;
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You might need to be careful with big files (>2 or 4Gb) and whatever method you use to rotate/backup log files needs to be aware of your seek position too.