RE: Date in perl

Tom Allison wrote:
> Gomez, Juan wrote:
>> I have a problem need to work with date
>>
>> I have a input like these : 20050829 and I need to change it to
>> something like this : Aug 29 2005
>>
>> but it still eludes me how to do that
>>
>> can anyone help me please?
>>

> I was going to say "use regex" but then I saw this nice example of
> unpack which should be faster.
>
> So I tested it:
> And ended up with this:
>
> tallison@isengard:~$ benchmark.pl
> Benchmark: timing 1000000 iterations of regex, unpack...
> regex: 2.75194 wallclock secs ( 2.75 usr + 0.00 sys = 2.75
> CPU) @ 363636.36/s (n=1000000)
> unpack: 2.15273 wallclock secs ( 2.15 usr + 0.00 sys = 2.15
> CPU) @ 465116.28/s (n=1000000)
>
> I think the POSIX modules would be considerably slower but I did not
> test them.

If absolute speed is essential Juan should load up an array with a month
number -> month name index and use substr to extract the month, day and
year values out of the string, i.e. months[0] = 'Jan', months[1] =
'Feb'....

However, if his date string may change I'd use strftime() with substr().

use strict;
use warnings;
use POSIX qw/strftime/;
use Benchmark ':hireswallclock';

my $string = '20050829';
timethese(1000000, {
'regex' => sub { my @array = $string=~/(\d\d\d\d)(\d\d)(\d\d)/;},
'unpack'=> sub { my @array = unpack('A4A2A2', $string); },
'substr'=> sub { my @array = (substr($string, 0, 4),
substr($string, 4, 2), substr($string, 6, 2)); },
});

print strftime('%b %d %Y', 0, 0, 0, substr($string, 6, 2),
substr($string, 4, 2) - 1, substr($string, 0, 4) - 1900);

Outputs:
Benchmark: timing 1000000 iterations of regex, substr, unpack...
regex: 12.1695 wallclock secs (11.59 usr + 0.00 sys = 11.59 CPU) @
86303.62/s (n=1000000)
substr: 5.70029 wallclock secs ( 5.54 usr + 0.00 sys = 5.54 CPU) @
180603.21/s (n=1000000)
unpack: 10.2787 wallclock secs (10.13 usr + 0.00 sys = 10.13 CPU) @
98765.43/s (n=1000000)
Aug 29 2005
.