my $alpha  = 'J';
my $num    = '3';

$alpha =~ /^ [[:alpha:]] $/x
and print 'correct';

$alpha !~ /^ [[:digit:]] $/x
and print 'correct';

$num  =~ /^ [[:digit:]] $/x
and print 'correct';

$num  !~ /^ [[:alpha:]] $/x
and print 'correct';