#!/usr/bin/perl
#
# usage: perl pickpart.pl startwhere onceevery infile outfile

my $startwhere = $ARGV[0];
my $onceevery = $ARGV[1];
my $infile = $ARGV[2];
my $outfile = $ARGV[3];

open (IN,$infile);
open (OUT,">$outfile");
my $x;
for (my $i=0; $i<$startwhere; $i++)
{
    $x = <IN>;
    print OUT $x;
}

while ($x = <IN>)
{
  if (rand($onceevery) < 1)
  {
      print OUT $x;
  }
}