Well it is trivial to make mine case insensitive. And I think mine makes better sense. Your routine considers 1.3 < 1.3a < 1.3a.2 but refuses to compare 1.3.4 to 1.3a.2. That seems inconsistant to me. I think that mine agrees with yours in all cases where yours will make a comparison.

Mine works for lots of types of strings but not strings that contain control characters, negative numbers, digit strings larger than 0.5G, numbers with embedded commas, numbers in scientific notation, fractions, or numbers with different numbers of digits after the decimal point.

There are quite a few variations on this "theme" that I've used at different times. If you need to support numbers of around 8000 digits, then you can use this one (that also ignores case):

sub compare_versions {
    my( $left, $right )= map lc, @_;
    for(  $left, $right  ) {
        s/(\d+)/pack("n",length$1).$1/ge;
    }
    return  $left cmp $right;
}
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I think yours does support differing number of digits in a part; e.g. 3.9 vs 3.10.

As for error checking, which is larger: 3.2 or 3B or i3r2 ?

Yes, it supports comparing versions were 3.10 comes after 3.9 (because 3.9==3.09), but it doesn't support decimal numbers where 3.10 comes before 3.9 (because 3.9==3.90) [but if the decimal numbers that will be compared together always have the same number of digits after the decimal (as is often the case), then it works]. Obviously it can't support both version strings and all decimal numbers, I just mentioned that because it is a general-purpose "natural sort".

Well, I definitely consider 3B to be a revision to the base branch and so 3B comes after 3.2. But I supposed some may disagree with me. So rejecting such comparisons is a worthwhile feature that can't be duplicated by a simpler method. (:

        - tye (but my friends call me "Tye")