# the original number of integers to test (will be one-upped)
my $i = 1; 

# the input string to be tested (a number)
my $foo = shift;

# see if the input string is a two-digit number
my $rc = ($foo =~ m{ \b (??{ ++$i; qr{\d{$i}}; }) \b }xmsg) ?'Y' :'N';