查找一個月的第三個星期日之前的星期一

Question

如何在shell腳本中爲接下來的N個月生成「本月第三個星期一前的星期一」列表？

date識別相當廣泛的一組操作（today + 3 months，例如），但我還沒有發現任何適合我的需要。

任何使用常見的GNU和BSD命令都可以。一個bash特定的答案也可以。

Answer 1

這只是一個月的第一天16 - '%u'。

expr `date -d"$year-$month-1" +'16 - %u'` 

%u day of week (1..7); 1 is Monday

Answer 2

使用GNU date：

$ cat mon-before-3rd-sun.sh 
mon_before_3rd_sun() 
{ 
    local year=$1 
    local mon=$2 
    local seconds weekday 

    # get the 1st day of the month 
    seconds=$(date +%s -d $year-$mon-1) 

    # weekday of the 1st day of the month 
    weekday=$(date +%u -d @$seconds) 

    # 1st Sunday of the month 
    ((seconds += (7 - weekday) * 86400)) 

    # Monday before 3rd Sunday (i.e. after 2nd Sunday) 
    ((seconds += 8 * 86400)) 
    date '+%Y-%m-%d' -d @$seconds 
} 

for ((mon = 1; mon <= 12; ++mon)); do 
    mon_before_3rd_sun 2015 $mon 
done 
$ bash mon-before-3rd-sun.sh 
2015-01-12 
2015-02-09 
2015-03-09 
2015-04-13 
2015-05-11 
2015-06-15 
2015-07-13 
2015-08-10 
2015-09-14 
2015-10-12 
2015-11-09 
2015-12-14 
$ 

Answer 3

這個怎麼樣（有道歉的長變量名，雖然這更多的是比教學效率）

#!/bin/bash 

function getMonBefore3rdSunInMonth 
{ 
    # Get the date N months from today. 
    monthN=$(date --date="+ ${1} month" +"%m/%d/%Y") 
    # The number of days from that date to the first of the month. 
    daysSinceFirstofMonth=$(($(date --date="${monthN}" +"%d") - 1)) 
    # The week-day of first of that month (0..6); 0 is Sunday 
    weekDayFirstOfMonth=$(date --date="${monthN}- ${daysSinceFirstofMonth} days" +"%w") 
    # The number of days between the given date and the Monday before 
    # the third Wednesday of the month (start at the begining of the month 
    # add an offset to the first Sunday, add 14 days to get to third and 
    # take off 6 days to get back to previous Monday. 
    offsetToMonBefore3rdSunInMonth=$((-${daysSinceFirstofMonth} + ((7 - ${weekDayFirstOfMonth}) % 7) + 14 - 6)) 
    # Use the offset to work out the date. 
    monBefore3rdSunInMonth=$(date --date="${monthN} + ${offsetToMonBefore3rdSunInMonth} days" +"%m/%d/%Y") 
    echo ${monBefore3rdSunInMonth} 
} 

N=${1} 
for n in $(seq ${N}) 
do 
    getMonBefore3rdSunInMonth $n 
done 

$ ./getMonBefore3rdSunInMonth.sh 12 
07/13/2015 
08/10/2015 
09/14/2015 
10/12/2015 
11/09/2015 
12/14/2015 
01/11/2016 
02/15/2016 
03/14/2016 
04/11/2016 
05/09/2016 
06/13/2016