Perl script to filter sites with more than 50 percent sites missing by population

In certain cases, its required to have sites from a VCF file filtered by fraction of genotypes missing by population. While entire sites can be filtered using programs like VCFtools, its not possible to filter them by population. Here its assumed that all individuals from $ARGV[1] to $ARGV[2] are in one population and those from $ARGV[3] to $ARGV[4] are in another.

 #!/usr/bin/perl  
 use List::Util qw[min max];  
 # Input parameters  
 my $vcf_file = $ARGV[0];  
 my $firstmissing=0;  
 my $firstall=$ARGV[2]-$ARGV[1];  
 my $secondmissing=0;  
 my $secondall=$ARGV[4]-$ARGV[3];  
 #Go through fasta file, extract sequences  
 open(IN, $vcf_file);  
 while($z=<IN>) {  
 $firstmissing=0;  
 $secondmissing=0;  
      if($z=~m/^#/){print $z;}  
      else{  
           chomp $z;  
           @values=split(/\t/,$z);  
      $totind=length @values;  
      for($i=$ARGV[1];$i<=$ARGV[2];$i++){if($values[$i]=~m/\.\/\./){$firstmissing++;}}  
      for($i=$ARGV[3];$i<=$ARGV[4];$i++){if($values[$i]=~m/\.\/\./){$secondmissing++;}}  
 if((($secondmissing/$secondall)<0.5)&&(($firstmissing/$firstall)<0.5)){print "$z\n";}  
      }#end of else #  
 }#end of file while  
 close IN;