In that case, changing the comparison operator has changed the way your sort works (effectively breaking it).

To demonstrate, try this code:

($a, $b) = ( '16:46:36', '16:00:00');

print 'cmp : ', $a cmp $b, "\n";
print '<=> : ', $a <=> $b, "\n";
[download]

This prints

cmp : 1
<=> : 0
[download]

Which shows that Perl thinks that the two strings are the same when using <=>. When doing a string comparison, Perl uses all of the characters in the string, but when doing a numeric comparison, it can only use the digits at the start of the string. It stops when it finds the first non-digit. Had you been using -w then you would have got a warning explaining what you were doing wrong.

Also, doing a string comparison on dates in the format "Jun 28, 2001" is a bad idea as it will do an alphabetical sort - not in date order.

I'd recommend doing a first pass on the data and converting it to YYYYMMDDhhmm, which you can then do a numeric sort on.

--
<http://www.dave.org.uk>

Perl Training in the UK <http://www.iterative-software.com>