Using sprintf to stringify a number, you may want to check its range to avoid negatives or overflow surprises: 
    my $id = shift;
    # disallow ID 0;
    $id > 0 && $id < 1e9 or return q();
    $id = sprintf '%0*lu', ($id < 1e6 ? 6 : 9), $id;
    ...

[download]
Or, you could let perl stringify the number, and munge it from there. 
sub id2path {
    my $id = shift;
    # allow ID 0; disallow 12.34
    $id =~ m/^\d{1,9}$/ or return q();
    my $n = length($id) > 6 ? 3 : 2;
    $id = sprintf '%0*s', 3 * $n, $id;
    $_ = "/$_/" for substr($id, $n, $n);
    # or: substr($id, $_, 0, '/') for -2*$n, -$n;
    return $id;
}

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Interestingly, perl sprintf allows zero-padding of %s! Is this a documented feature?

In reply to Re: Can you make it nicer? by oiskuu
in thread Can you make it nicer? by choroba

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