use strict;
use warnings;

# setup bounds
my @digits = ( 0 .. 9 );
my $min_digits = 4;
my $max_digits = 6;

# build the glob string
my $glob_string;
for my $dignum ( 1 .. $max_digits ) {
    if ( $dignum <= $max_digits - $min_digits ) {
        $glob_string .= '{' . join( ',', ( '', @digits ) ) . '}';
    }
    else {
        $glob_string .= '{' . join( ',', @digits ) . '}';
    }
}

# print the permutations
my $num;
while ( $num = glob( $glob_string ) ) {
    print $num, "\n";
}