Hmm, that is a bit over-complicated.

See Spreadsheet::Read::cell2cr:

# cell2cr ("D18") => (4, 18)
sub cell2cr {
    ref $_[0] eq __PACKAGE__ and shift;
    my ($cc, $r) = (uc ($_[0]||"") =~ m/^([A-Z]+)([0-9]+)$/) or return
+ (0, 0);
    my $c = 0;
    while ($cc =~ s/^([A-Z])//) {
        $c = 26 * $c + 1 + ord ($1) - ord ("A");
        }
    ($c, $r);
    } # cell2cr
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update:

haukex is correct, as always. Sorry for not reading more closely.

Look at col2label instead:

# col2label (4) => "D"
sub col2label {
    ref $_[0] eq __PACKAGE__ and shift;
    my $c = shift;
    defined $c && $c > 0 or return "";
    my $cell = "";
    while ($c) {
        use integer;

        substr $cell, 0, 0, chr (--$c % 26 + ord "A");
        $c /= 26;
        }
    $cell;
    } # col2label
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