my $chunksize = 500 * 1024; # 500Kb
my $filenumber = 0;
my $infile = "infile.dat";
my $outsize = 0;
my $eof = 0;

open INFILE, $infile;
open OUTFILE, ">outfile_".$filenumber.".dat";

while(<INFILE>)
{
        chomp;

        $outsize++;
        if( $outsize>$chunksize and /^.{67}11/ )
        {
                close OUTFILE;
                $outsize = 0;
                $filenumber++;
                open (OUTFILE, ">outfile_".$filenumber.".dat") or die "Can't open outfile_".$filenumber.".dat";
        }

        print OUTFILE "$_\n";
        $outsize += length;

}
close INFILE;