#!/usr/bin/perl -T

use strict;
use warnings;

use Scalar::Util qw(tainted);

# Run this as "perl -T test.pl hello" or similar, so $var is "from outside"
my $var = shift;

# Uncomment the following line to untaint $var and see 'normal' behaviour of pos()
# $var =~ /(.*)/; $var = $1;	# Untaint blindly, don't do this in real code

# Report whether $var is tainted or not
print "Var is " . (tainted($var) ? "tainted" : "not tainted") . "\n";

# Odd behaviour only arises when tainted $var is in an array
my @array = ($var);

# If this matches, then pos() should be set to 1
$array[0] =~ /./gc	and print "Match found";

# Check what pos() actually IS set to... 
my $pos = pos($array[0]) // 'UNDEF';
print "Pos is now $pos\n";