LAST DAY

LAST_DAY
last day of month
last_of_month

test set

input: 2011-11-11

output: 2011-11-30

1 Bash

INPUT=2011-11-11
LAST_DAY=`date +%Y-%m-%d -d "$INPUT +1 month -${INPUT:8:2} days"`
echo $LAST_DAY

2 PHP

$date = "2011-11-11";
$last_day = date('Y-m-d', mktime(0, 0, 0, substr($date,5,2)+1, 0, substr($date,0,4)));
// 2011-11-30

function last_day($day) {
  return date('Y-m-d', mktime(0, 0, 0, substr($day,5,2)+1, 0, substr($day,0,4)));
}

3 SQL

3.1 MySQL

SELECT LAST_DAY( "2011-11-11" );

3.2 Oracle

SELECT LAST_DAY(TO_DATE('2007-12-15', 'yyyy-mm-dd')) FROM DUAL;
-- returns 2007/12/31 00:00:00

SELECT TO_CHAR(LAST_DAY(TO_DATE('2011-02-22', 'yyyy-mm-dd')), 'yyyy-mm-dd') FROM DUAL;
-- returns 2011-02-28

4 See also