#!/usr/bin/env -S perl -T
use strict;
use warnings;
use 5.020;
use Scalar::Util qw(tainted);

sub untaint_unchecked {
    ($_[0] =~ /(.*)/)[0];
}

sub check_taint {
    my ($name,$var) = @_;;
    my $tainted = tainted($var) ? '' : ' nicht';
    say "$name mit Wert '$var' ist$tainted verdorben";
}

check_taint("Umgebungsvariable HOME", $ENV{HOME});

my $var = $ENV{HOME} =~ s!/!::!gr;
check_taint("Modifizierte Kopie",$var);

my $laundered = untaint_unchecked($var);
check_taint("Reingewaschene Variable",$laundered);