#!/usr/bin/perl

use strict;
use POSIX qw(tmpnam);

my $file = shift or die "Usage: $0 filename <filesize>\n";

my $filesize  = shift || 100000;

open(F, "+<$file") or die "Could not open $file: $!\n";

my @files;
my $outfile = "aaaa";

{

  open(OUTFILE, ">$outfile") or die "Could not write $outfile: $!\n";
  select((select(OUTFILE),$|++)[0]);

  my $C;
  sysseek(F,-$filesize,2) or sysseek(F,0,0);
  sysread(F,$C,$filesize); ## should check return value...
  sysseek(F,-$filesize,2) or sysseek(F,0,0);
  truncate(F,sysseek(F,0,1));
  print OUTFILE $C;
  close(OUTFILE);
  unshift(@files, $outfile);

  last unless -s $file;

  ## We need a new filename
  {
    my $x = 1;
    1 while substr($outfile,-$x++,1) eq "z";
    if (--$x > length $outfile) { $outfile = tmpnam(); }
    else {
      substr($outfile,-$x--,1)++;
      substr($outfile,-$x--,1) = "a" while $x;
    }
    redo if -e $outfile;
  }

  redo;
}

my $files = @files;
print "Files created: $files\n";

if ($files>1) {
  my $meow = tmpnam();
  select(CATS) if open(CATS, ">$meow");
  print "cat ", join(" ", @files), " > $file\n";
  print STDOUT "Re-create with $meow\n";
}