$re = qr/$regex/;

$_ =~ $re;

##</code><code>##

use Benchmark;

sub make_grep {
    my $p = $_[0];
    eval "sub { grep /$p/o, @_ }";
}

sub make_grep2 {
    my $p = $_[0];
    sub { grep /$p/o, @_ };
}
$re = '(ob|[tTs])';
$a = make_grep($re);
$b = make_grep2($re);
$pat = qr/$re/;

timethese(100000,
{
    a => sub { $a->(qw(this is a test bob and jobe)) },
    b => sub { $b->(qw(this is a test bob and jobe)) },
    c => sub { grep $pat, qw(this is a test bob and jobe) }
});

##</code><code>##

Benchmark: timing 100000 iterations of a, b, c...
         a:  7 wallclock secs ( 5.92 usr +  0.00 sys =  5.92 CPU) @ 16891.89/s (
n=100000)
         b:  5 wallclock secs ( 4.57 usr +  0.00 sys =  4.57 CPU) @ 21881.84/s (
n=100000)
         c:  0 wallclock secs ( 0.62 usr +  0.00 sys =  0.62 CPU) @ 161290.32/s
(n=100000)