#!/usr/bin/perl -T
 
use strict;
use warnings;
 
# taken from Programming Perl, 3rd edition, p 561
sub is_tainted {
   my $arg = shift;
   my $nada = substr($arg, 0, 0);
   local $@;
   eval { eval "# $nada" };
   return (length($@) != 0) ? 'tainted' : 'not tainted';
}
 
my %hash = ();
open FILE, $0 or die "cannot open $0: $!";
while (my $line = <FILE>) {
   chomp $line;
   warn is_tainted($line);
   $hash{$line} = is_tainted($line);
}
close FILE;
 
foreach my $key (keys %hash) {
   warn is_tainted($key);
}