#!/usr/bin/perl

# 30431731 data.csv
# 33973479 plz " " ähnlich
# 33988862 gesamt

for my $pfx (100 .. 9999) {
   $pfx = sprintf "%04d", $pfx;
   my $plz = sprintf "data/%04d.txt.gz", $pfx;
   -e $plz or warn $plz;
   20 < -s $plz or next;
   open D, "gzip -cd $plz |"
      or die;
   my $x = <D>;
   $x =~ /,"$pfx\d",/ or warn "$plz $x";
}