perldoc Scalar::Util|grep taint

        use Scalar::Util qw(blessed dualvar isweak readonly refaddr reftype tainted weaken isvstring looks_like_number set_prototype);
    tainted EXPR
        Return true if the result of EXPR is tainted
            $taint = tainted("constant");       # false
            $taint = tainted($ENV{PWD});        # true if running under -T