PHP获得本周、本月、上周、上月起始时间戳

<?php
// 今日起止时间
$beginToday = mktime(0,0,0,date('m'),date('d'),date('y'));
$now = time();

//昨天起至时间
$beginYesterday = mktime(0,0,0,date('m'),date('d')-1,date('y'));
$endYesterday = mktime(0,0,0,date('m'),date('d'),date('y'))-1;

//本周起止时间
$beginThisweek = mktime(0,0,0,date('m'),date('d')-date('w')+1,date('y'));
$now = time();

//上一周起止时间
$beginLastweek = mktime(0,0,0,date('m'),date('d')-date('w')-6,date('y'));
$endLastWeek = mktime(23,59,59,date('m'),date('d')-date('w'),date('y'));

//本月起至时间
$beginThismonth = mktime(0,0,0,date('m'),1,date('y'));
$now = time();

//近三个月起止时间
$beginLastThreemonth = mktime(0,0,0,date('m')-3,1,date('y'));
$now = time();
?>