Looks like you are counting base 3, but with every digit plus 1, i.e. 0000 becomes 1111 and 2222 becomes 3333

#!/usr/bin/perl

use warnings;
use strict;

my $length=4;

my @number= (1) x $length;

while (@number) {
    printnumber(@number);
    @number= addto(@number); 
}



sub addto {
    my @number= @_;
    while (1) {
    my $carry=1;
    foreach (@number) {
        $_+= $carry; $carry=0;
        if ($_>3) {
        $_=1;
        $carry=1;
        }
    }
    @number=() if ($carry==1);
    return(@number);
    }
}

sub printnumber {
    my @number= @_;
    print reverse(@number),"\n";
}
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Your problem is a bit underspecified in that it is not clear if $length should also be a limit to the digits you use. I assumed not.