Question

I was wondering if there is an in-built Perl function that adjusts the date if you take a month from it. E.g. if date is the 31st, it will adjust to be the end of the previous month if it doesn’t have 31 days.

I would just change it to 30th easily if it weren’t for the months with 31 days next to each other (Dec/Jan, Jul/Aug) and February.
I just want to store the date a certain amount of time away from the current date, e.g.

my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);

$current_date = join("-", (1900+$year), ($mon+1), $mday);
$one_month_ago = join("-", (1900+$year), ($mon), $mday);
$one_year_ago = join("-", (1899+$year), ($mon+1), $mday);

I can deal with the February instance as it only applies to years, but if this was taken on the 31st December 2012 then taking away a month would mean 31st Nov 2012, which of course didn’t exist. I thought I would ask if there was a function before complicating things for myself… thanks 🙂

Answer 1

Others have suggested DateTime, but it’s quite large, non-core, and can be slow.

A much simpler solution is to use the builtin localtime and POSIX::mktime functions:

use POSIX qw( mktime );

my @t = localtime $epoch;
$t[4] -= 2;  # $t[4] is tm_mon
my $two_months_ago = mktime @t;

The mktime() function specifically handles denormalised values; it will cope with the fact that Janurary minus 2 months is November of the previous year, etc.. It will keep the same second/minute/hour of the day, and the same day of the month.