#!/usr/local/bin/perl -Tw
#
#   $Id: yesterday,v 1.2 2000/09/26 18:59:29 dgregor Exp $
#
# yesterday -- figure out yesterday's date
#	- Useful for scripts that rotate logs out of cron at midnight.
#
# By Daniel J. Gregor, Jr., <dj@gregor.com>
# Placed in the Public Domain on Wed Dec 16 01:40:27 EST 1998
#
# The goal is to accurately find out yesterday's date, so what we do is
# find the first second of today, sutract one, and we have yesterday. :)
# Thanks to localtime() and timelocal(), this is quite easy:
#	- Get current time from time(), convert to an array with localtime().
#	- Zero out the seconds, minutes, and hours values in the array.
#	- Convert the array back into seconds since epoch.
#	- Subtract one from the previous value, and we are now in yesterday
#	  (I hope there aren't any exceptions to this).
#	- Convert back to an array, zero out seconds, minutes, and hours,
#	  and we are now at the beginning of yesterday.
#	- Print out the fruits of our labor in a useful format.

use Time::Local;
use Getopt::Std;
use POSIX;

Getopt::Std::getopts('f:', \%opts);

# get current time
@timearray = localtime(time());

# set the seconds, minutes, and hours to zero
$timearray[0] = 0;	# seconds
$timearray[1] = 0;	# minutes
$timearray[2] = 0;	# hours

# we now have the first second of today
$time = Time::Local::timelocal(@timearray);

# now the last second of yesterday
@timearray = localtime($time - 1);

# set the seconds, minutes, and hours to zero
$timearray[0] = 0;	# seconds
$timearray[1] = 0;	# minutes
$timearray[2] = 0;	# hours

# first second of yesterday
$time = Time::Local::timelocal(@timearray);

# do something useful.... print out the time.
if (defined($opts{'f'})) {
	print POSIX::strftime($opts{'f'}, localtime($time)), "\n";
} else {
	print scalar(localtime($time)), "\n";
}