#!/usr/bin/perl -T

use File::Spec;
use Scalar::Util;

my $pathdir = $ENV{HOME};  # tainted, existing dir, absolute path
(-d $pathdir) and File::Spec->file_name_is_absolute($pathdir);

my $stuff = File::Spec->canonpath("foo/bar");
print "\nerror $stuff is tainted\n" if Scalar::Util::tainted($stuff);

sub foo {
    open(BAREWORD, "<foobar") || return;
    close(BAREWORD);
}