shell获取指定时间的月头,月尾,季头,季尾
月头: date -d "2014-01-07" +%Y-%m-01
月尾: date -d "`date -d '2014-01-07 +1 month ' +%Y-%m-01` -1 day " +%F
季头: date -d "`awk -F- '$2%3==1{print $1FS$2FS"01";next}$2%3==2{print $1FS$2-1FS"01";next}{print $1FS$2-2FS"01"}' <<<2014-1-07`" +%F
季尾: date -d "`awk -F- '$2%3==1{print $1FS$2+3FS"01";next}$2%3==2{print $1FS$2+2FS"01";next}{print $1FS$2+1FS"01"}' <<<2014-1-07` -1 day" +%F