use strict;
use Test::More 'no_plan';

my $rx = qr/\A
    (?: [0-4]\d? | 5?[0-5] ) \.
    (?: [0-4]\d? | 5?[0-5] )
\z/x;

my %test = (
    '56.0' => 0,
    '0.56' => 0,
   '48.56' => 0,
   '56.10' => 0,
    '55.0' => 1,
   '55.55' => 1,
     '0.0' => 1,
   '10.10' => 1,
);

my $result;

is(/$rx/, !!$result, $_) while ($_, $result) = each %test;

__END__
ok 1 - 0.56
ok 2 - 56.10
ok 3 - 55.0
ok 4 - 55.55
ok 5 - 48.56
ok 6 - 56.0
ok 7 - 10.10
ok 8 - 0.0
1..8