Have a look at sprintf for your leading zeros. Others have mentioned closures or subroutines incrementing a global variable. IMHO a closure is tidier, obviating the need for a global that might accidentally get tinkered with elsewhere in the code.

knoppix@Microknoppix:~$ perl -Mstrict -wE '
> my $rcIncrement = do {
>    my $value = 0;
>    sub { return sprintf q{%03d}, ++ $value };
>    };
> 
> say $rcIncrement->() for 1 .. 3;
> say q{-} x 10;
> say $rcIncrement->() for 1 .. 3;'
001
002
003
----------
004
005
006
knoppix@Microknoppix:~$
[download]

I hope this is helpful.