use strict;
use warnings;

## buffering off
++$|;

## for storing numbers entered so far
my %hsh;

while (1){
	print "Enter something (or nothing if you are bored):\n";
	## get input
	my $num = <>;
	chomp $num;
	## exit infinite loop if the user hits enter twice
	last if (!defined$num || $num eq '');
	
	## check against previous input
	if (exists $hsh{$num}){
		print "Seen >$num< before, try again.\n";
		next; 
	}
	else {
		print "Oooh >$num< is new, thanks!\n";
		++$hsh{$num};
	}
}

print +(join "\n\t", "Finished! You entered :", sort keys %hsh);

##</code><code>##

Enter something (or nothing if you are bored):
4
Oooh >4< is new, thanks!
Enter something (or nothing if you are bored):
foo
Oooh >foo< is new, thanks!
Enter something (or nothing if you are bored):
bar
Oooh >bar< is new, thanks!
Enter something (or nothing if you are bored):
4
Seen >4< before, try again.
Enter something (or nothing if you are bored):

Finished! You entered :
	4
	bar
	foo