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Re: sorting dates in YYYYMMDD format

by Dallaylaen (Scribe)
on Jul 04, 2013 at 12:30 UTC ( #1042448=note: print w/ replies, xml ) Need Help??

in reply to sorting dates in YYYYMMDD format

I've turned on warnings because I didn't get what's wrong with your code (which looks correct at first glance) and suddenly...

-bash$ xsel -o | perl -w Name "main::d" used only once: possible typo at - line 9. Use of uninitialized value $d in numeric comparison (<=>) at - line 9. Use of uninitialized value $d in numeric comparison (<=>) at - line 9. 20130601 20130501 20130401

It looks like $d is never initialized in the first place, and evaluates to 0 in a numeric comparison. So to make life a bit easier, I would suggest always turning on strict and warnings:

#!/usr/bin/perl use strict; use warnings; # or just #!/usr/bin/perl -w on first line my @dates = ('20130401', '20130501', '20130601'); my @ordered = sort { &compare } @dates; print "@ordered\n"; sub compare { $a =~ /(\d{4})(\d{2})(\d{2})/; my $c = $3 . $2 . $1; $b =~ /(\d{4})(\d{2})(\d{2})/; my $d = $3 . $2 . $1; $c <=> $d; }
And now typing $c instead of $d makes program crash on the compilation stage, instead of silently corrupting data. Also note the "my" keyword - in strict mode you have to declare your variables, instead of just using them (and probably destroying previous data). ($a and $b are special vars that require no "my" though).

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