#!/usr/bin/perl
$nlskip=$ARGV[ 0 ]; # number of lines skipped
$ifn=$ARGV[ 1 ]; # input file name
$ofn=$ARGV[ 2 ]; # output file name
$maxlinesize= 256 ; # expected maximum line length
$chunksize= 1024 * 1024 ; # chunk size for read/write operations
$filesize=(stat($ifn))[ 7 ];
$tailoffset=$nlskip*$maxlinesize;
$tailoffset=$filesize if $tailoffset>$filesize;
open(IFN,"<$ifn")||die("Can't open source file $ifn");
seek(IFN,$filesize-$tailoffset,0);
sysread(IFN,$buffer,$tailoffset);
for($n=$tailoffset-1;$n>0;$n--){
    if(substr($buffer,$n,1) eq "\n"){
	if(--$nlskip<0){
	    $lastoffset=$filesize-($tailoffset-$n);
	    seek(IFN,0,0);
	    open(OFN,">$ofn")||die("Can't create target file $ofn");
	    for($offset= 0 ;;){
		$nread=$lastoffset-$offset;
		$nread=$chunksize if $nread>$chunksize;
		sysread(IFN,$buffer,$nread);
		syswrite(OFN,$buffer);
		$offset+=$nread;
		exit  0   if $nread<$chunksize;
	    }
	}
    }
}