A common version number contains sequences of digits, sequences of letters, and punctuation marks.

The string is viewed as a sequence of components. The components are compared with corresponding components, from left-to-right.

A component is one of the following:

• A series of digits. They are compared as numbers (“11” > “2”).
• A series of ASCII letters. They are compared as strings, case-insensitive.
• A series of punctuation marks, loosely defined as everything else. They are compared as match/no-match only. A no-match is considered an exception, and prevents greater/less comparisons from working at all.

The parts are compared from left-to-right. If the parts match up to the point where one string runs out of parts, the one with parts left over is Larger. For example, “1.23.45” < “1.23.45b”. The left string has 5 parts (3 series’ of digits, two series’ of punctuation marks); the right string has 6 parts.

Strings that don’t work with this algorithm are those that use words, dates, or non-left-to-right ordering of parts.

This was written before Perl provided the "v-string" literal. But, it is not limited to just numbers and dots. It handles most any reasonable version naming system, including other delimiters and letters as well as numbers.

{
my $splitter= qr/\d+|[A-Za-z]+|[^0-9A-Za-z]+/;
sub compare_version_string ($$)
# returns <0, 0, >0 to indicate less, eq, or greater-than.
# dies (exception) if no relation exists.
 {
 my ($left, $right)= @_;
 my @left= $left =~ /$splitter/g;
 my @right= $right =~ /$splitter/g;
 print "@left\n";
 print "@right\n";
 my $r;
 while (@left && @right) {
    $left= shift @left;
    $right= shift @right;
    if ($left =~ /^\d+$/ && $right =~ /^\d+$/) {
       # compare as numbers
       $r= $left <=> $right;
       return $r  if $r;  # or keep going if zero.
       }
    elsif ($left =~ /^[A-Za-z]+$/ && $right =~ /^[A-Za-z]+$/) {
       # compare as strings
       $r= $left cmp $right;
       return $r  if $r;  # or keep going if zero.
       }
    elsif ($left =~ /^[^0-9A-Za-z]+$/  &&  $right =~ /^[^0-9A-Za-z]+$/
+) {
       # delimter or "other", much match exact.
       die "version strings are not compatible.\n"  unless $left eq $r
+ight;
       }
    else {
       # the parts are not of the same type
       die "version strings are not compatible.\n";
       }
    }
 # one of the strings ran out of parts.
 return scalar(@left) <=> scalar(@right);
 }
}
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