PHP 获取前月 月初/月末 日期

$now = '2021-03-30';
echo 'now： '.$now.'<br><br>';

$firstDayOfThisMonth = date("Y-m-01", strtotime($now));
echo 'first day of this month： '.$firstDayOfThisMonth.'<br><br>';

$lastDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 day'));
echo 'last day of prev month： '.$lastDayOfPrevMonth.'<br><br>';


$firstDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 month'));
echo 'first day of prev month： '.$firstDayOfPrevMonth.'<br><br>';

echo '------------------------------------<br><br>';
$now = '2021-10-01';
echo 'now： '.$now.'<br><br>';

$firstDayOfThisMonth = date("Y-m-01", strtotime($now));
echo 'first day of this month： '.$firstDayOfThisMonth.'<br><br>';

$lastDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 day'));
echo 'last day of prev month： '.$lastDayOfPrevMonth.'<br><br>';


$firstDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 month'));
echo 'first day of prev month： '.$firstDayOfPrevMonth.'<br><br>';

echo '------------------------------------<br><br>';
$now = date("Y-m-d");
echo 'now： '.$now.'<br><br>';

$firstDayOfThisMonth = date("Y-m-01", strtotime($now));
echo 'first day of this month： '.$firstDayOfThisMonth.'<br><br>';

$lastDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 day'));
echo 'last day of prev month： '.$lastDayOfPrevMonth.'<br><br>';


$firstDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 month'));
echo 'first day of prev month： '.$firstDayOfPrevMonth.'<br><br>';

echo '------------------------------------<br><br>';

**

测试结果

**

now： 2021-03-30

first day of this month： 2021-03-01

last day of prev month： 2021-02-28

first day of prev month： 2021-02-01

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now： 2021-10-01

first day of this month： 2021-10-01

last day of prev month： 2021-09-30

first day of prev month： 2021-09-01

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now： 2021-12-23

first day of this month： 2021-12-01

last day of prev month： 2021-11-30

first day of prev month： 2021-11-01

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