topic Re: Date computation in a shell script in Operating System - HP-UX

Date computation in a shell script

Bala_4 — Thu, 27 Sep 2001 21:28:20 GMT

Hi All

Is there a way to add/subtract days using date function in a shell script ?
Please don't tell me that I have to write lengthy unix script .

for e.g I want to add 2 days to the current date in a shell script !!!
i.e expr "`date + 2`" or something like that

Thanks in advance

Bala

Re: Date computation in a shell script

someone_4 — Thu, 27 Sep 2001 21:36:44 GMT

This has been asked before here is one link i found that should help you out.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0x5fc3854994d9d4118fef0090279cd0f9,00.html

Re: Date computation in a shell script

A. Clay Stephenson — Thu, 27 Sep 2001 21:39:10 GMT

Hi:

I have a simple utility that makes this duck soup. The script is complicated but it's already written - so who cares.

The idea is that we convert today's date to a true Jukian Day (~ num of days since 4004 BCE) and add 2 to it and then send that number back in to the script.

TODAY=`caljd.sh`
NEXTDATE=$((${TODAY} + 2))
NEWDATE=`caljd.sh ${NEXTDATE}`
echo ${NEWDATE}.

The attached script does all the hard work and if you execute caljd.sh -u it will display the full usage. The neat thing about this method is that it will work across months, leap years,
past or future, ...

Regards, Clay

Re: Date computation in a shell script

Jeffrey S. Sims — Thu, 27 Sep 2001 21:41:50 GMT

No long UNIX script just a simple line of perl

perl -e 'print scalar localtime (time +2 * 86400),"\n"'

will add 2 days to the current date

perl -e 'print scalar localtime (time -2 * 86400),"\n"'

will subtract 2 days from the current date

Hope this helps

Re: Date computation in a shell script

Sridhar Bhaskarla — Thu, 27 Sep 2001 21:45:23 GMT

Bala,

Unfortunately there is no single command to do arthmetic on dates. There are quite a number ways to do this. As perl is almost there on unix systems, you can use the method suggested by David in the thread

http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0x2fc2854994d9d4118fef0090279cd0f9,00.html

or you can use the logic behind it.

-Sri

Re: Date computation in a shell script

Bala_4 — Thu, 27 Sep 2001 21:53:13 GMT

Thanks Everyone for the quick replies...

Thanks again

Bala