friday before the last Tuesday of the month -- script

Dafydd · 09-23-2014, 05:18 PM

I need a script that 'cron' can read and if it is the Friday before the last Tuesday of each month, call another script that will send an email.

I know how to set up 'cron'. I have the emailing code, all I need it how to figure out the date.

I have done this before using BRUTE FORCE simuler to this faux code example.

Code:

read date
if month == 'September' && day == '22'; then send = True
	elif
		.......
	elif
		.......
	elif
		.......

This will need to be updated each year. Is there an algorithm that will calculate this. So I can put this function in a file and not have to worry about it for 10 years.

Where should I go, or what should I Google for information on this subject?

suicidaleggroll · 09-23-2014, 05:29 PM

What if you do something along the lines of

Code:

if (today == 'Friday') &&
   month(today) == month(today+4 days) &&
   month(today) != month(today+11 days)
do stuff

Pseudocode obviously, but the logic should be sound and it should be very easy to implement with date's format code and -d flag.

today == 'Friday' ensures that today is Friday (obviously)
month(today) == month(today+4) ensures that the following Tuesday is still part of the same month
month(today) != month(today+11) ensures that the following Tuesday is the last Tuesday in the month

edit: something along the lines of

Code:

thisday=$(date +%u)
thismon=$(date +%m)
thisp4mon=$(date -d "+4 days" +%m)
thisp11mon=$(date -d "+11 days" +%m)

if [[ $thisday -eq 5 && $thismon -eq $thisp4mon && $thismon -ne $thisp11mon ]]; then
   echo "This is the Friday before the last Tuesday of the month!"
fi

michaelk · 09-23-2014, 07:11 PM

It would be easier to determine the last Tues of the month and subtract 4. You can find many examples of finding a certain day of the week but set the cron job to run the script on Tuesdays and then check the day of the month for >24 (I think this is correct). If true then it is the last Tues and in your script subtract 4 days instead of adding as above.

[ date "+%d" -gt 24 ] && /path/to/your/script

Not necessary to adjust for years...

suicidaleggroll · 09-23-2014, 07:38 PM

My interpretation of the problem is not that he needs to know what date the Friday before the last Tuesday of the month is, but that he needs to run the script on the Friday before the last Tuesday of the month. So checking whether "today" is the last Tuesday of the month doesn't really help, it just tells you that you should have run the script four days ago. Maybe I misunderstood the question.

You won't be able to check for date < 24 or any other fixed number, since the month could have 28, 29, 30, or 31 days. To take that approach, you would need to check the current month and reference a lookup table with the number of days in each month, in addition to checking whether or not it's a leap year if the month is February. It's doable, but seems much more complicated to me.

michaelk · 09-23-2014, 08:18 PM

Doh. your correct.

Dafydd · 09-24-2014, 12:12 AM

Thank you for the input and feed back. I will try it this coming Friday and report back.

Dave

AnanthaP · 09-25-2014, 12:03 AM

cal mm yyyy pipe to awk and derive (by comparison in each record) the max value of column 6 (friday). on END subtract 4 from it and send the value where you want it.

While testing, I added two selection conditions and the code becomes:

Code:

cal 09 2014 | awk 'NR>2 && NF>5 {if {$6>m) m=$6;} END(print m-3}'

I also tested it with arguments 10 2014 and 11 2014 to check for the end conditions and it worked fine.

OOPS sorry.
I just realized that I did "Tuesday before the last Friday". But the idea is OK. The code for "Friday before last Tuesday" becomes:

Code:

cal 09 2014 | awk 'NR>2 && NF>1 {if {$2>m) m=$2;} END(print m-4}'

To be tested.

OK

rknichols · 09-25-2014, 12:22 PM

Here is a script that will reliably print the date of the Friday preceding the last Tuesday of the current month. Hopefully the verbose variable names make it understandable. Run it with "bash -x ..." if it's still not clear.

Code:

#!/bin/bash
Tues=2
First_of_this_month=$(date +%Y-%m-1)
Next_month_begins_on=$(date -d "$First_of_this_month + 1 month" +%w)
Adj=$((Tues - Next_month_begins_on))
[ $Adj -gt -1 ] && Adj=$((Adj - 7))
FinalTue=$(date -d "$First_of_this_month + 1 month $Adj day" +%F)
PreviousFriday=$(date -d "$FinalTue - 4 days" +%F)

echo $PreviousFriday