#!/usr/bin/perl
my $delim="asdf";
$/=$delim;
open(FILE,"/some/big/file");
my $offset=0;
my $lastoffset=0;
for (;;) {
   <FILE>;
   my $offset=tell(FILE);
   last if eof(FILE); 
   print "this record spans [$lastoffset] to [$offset], including";
   print "the delimiter\n";
   print " this means you could seek to $lastoffset and read for ";
   printf "%d bytes to get the record\n",
       $offset-$lastoffset-length($delim);
   $lastoffset=$offset;
}