my $max = 700;
my %seen = ();
my $run = 1;
while($run) {
   my $lncount = 0;
   while(<IN>) {   
      my $r = int(rand(2));
      if($r == 0 and not exists $seen{$lncount}) {
         print OUT $_;
         $seen{$lncount} = 1;
         --$max;
         if($max == 0) {
             $run = 0;
             last;
         }         
      }
      ++$lncount;
   }
   seek(IN, 0, 0) if $run;
}

#!/usr/bin/perl

use strict;
use warnings;

my %hash  = ();
my $max   = 60_000;
my $count = 700;

while(keys(%hash) < $count-1){
  $hash{int rand($max)} = 1;
}

print scalar(keys(%hash));
print $_,"\n" for(keys(%hash));

#!/usr/bin/perl

use strict;
use warnings;
use Tie::File;

my %hash  = ();
my $file  = '/path/to/file.txt';
my $count = 700;

tie my @array,'Tie::File',$file or die $!;
while(keys(%hash) < $count-1){
  $hash{$array[int rand(scalar(@array)-1)]} = 1;
}
untie @array;

print scalar(keys(%hash));
print $_,"\n" for(keys(%hash));

my $max = 700;
my %seen = ();
my $run = 1;
while($run) {
   my $lncount = 0;
   while(<IN>) {   
      my $r = int(rand(2));
      if($r == 0 and not exists $seen{$lncount}) {
         print OUT $_;
         $seen{$lncount} = 1;
         --$max;
         if($max == 0) {
             $run = 0;
             last;
         }         
      }
      ++$lncount;
   }
   seek(IN, 0, 0) if $run;
}

my $r = rand(1);
if($r < 0.5 and not exists $seen{$lncount}) {