sub pad {
    my( $str, $width, $delim, $pad )= @_;
    $width= 3   if  ! defined $width;
    $delim= "."   if  ! defined $delim;
    $pad= "0"   if  ! defined $pad;
    return join $delim, grep {s/ /$pad/g;1}
        map {sprintf"%${width}s",$_}
        split /\Q$delim\E/, $str, -1;
}
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Use a negative width to pad in the other direction.

Update: Fixed a minor bug (my abuse of grep should have ended with ";1" not ";$_") and wanted to note that the transformation of " " to $pad when it is part of the original string but not part of a delimiter is a feature. ;)

Thanks. That's just what I was looking for.