assign yesterday's date in ksh

[satheeshnp]

I have a requirement to assign yesterday's date in to a var.This should be compatible with all the months from Jan to Dec.

I am using ksh. whether there is any command

[Anshumali]

Below should be helpful, many examples:
http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=9251

[James R. Ferguson]

Hi:

# YESTERDAY=$(perl -MPOSIX -le 'print strftime "%b %e",localtime(time-(60*60*24))')

# echo "${YESTERDAY}"
Oct 17

This will compute yesterday's date in your local timezone.

The Perl POSIX module allows you to use the 'strftime()' function with the same formatting directives you find in its manpages [ 'strftime(3C)' ]. These directives are the same as you use with the 'date' command. The '%e' specification yields the day of the month with space fill whereas the '%d' uses zero-fill.

Regards!

...JRF...

[mvpel]

A not-so-subtle way of saying scripts should be in Perl, not sh.

In order to do this in shell, I think you can manipulate the TZ variable - just add the proper number of hours to your current timezone offset, like so:

gbrhpq$ echo $TZ
EST5EDT
gbrhpq$ date
Wed Oct 20 18:02:19 EDT 2010
gbrhpq$ expr 5 + 18 + 1
24
gbrhpq$ TZ=EST24EDT
gbrhpq$ date
Tue Oct 19 23:08:09 EDT 2010
gbrhpq$

It looks like the trick is adding just enough hours to the timezone offset to take you back to sometime after 23:00 (11:00pm) the day before. If you add more, it goes back to the current date and time:

gbrhpq$ TZ=EST25EDT
gbrhpq$ date
Wed Oct 20 18:17:09 EDT 2010
gbrhpq$

I'm not sure if this will work at 7:00pm in the same way, though. We'll see...

[James R. Ferguson]

Hi (again):

> A not-so-subtle way of saying scripts should be in Perl, not sh.

There was no subtle message in what I wrote. I wasn't invoking a holy war; rather I was pointing out a pitfall that isn't necessarily apparent at first blush.

> In order to do this in shell, I think you can manipulate the TZ variable

Sure, fraught with peril. Oddly, if you look at *my* response to this technique in the link that Anshumali posted in this thread, you will see *why* using the TZ variable is a slippery slope.

Regards!

...JRF...