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How to get yesterday's date accurately using ksh?

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# 8  
Old 04-21-2011
Quote:
Originally Posted by kchinnam
vgersh99,

I did lot of searching and read lot of postings about this on this site and finally decided to use my own improved syntax
---> $(TZ=$(date +%Z)+24 date +%Y%m%d%H%M)

But I found a bug with this,, apparently this is putting yesterday's datetime 4 hrs ahead of what its supposed to be.

Please be patient and validate what I found. This is really important for scheduling jobs I am sure for many of us using older shells. I think its worth re-validating it.

Unless you print Hours and minutes you will not know what this is giving is true or not. Or test this after 10 PM.
Once again, check out the posted link to the FAQ session - no need to reinvent the wheel (as it will most likely come out squared).
# 9  
Old 04-21-2011
Quote:
Originally Posted by kchinnam
cambridge,
That is incredible. Your solution is not only 100% correct, it also formats it.
Glad to be of service.

Quote:
I am still looking for a reason why the ksh syntax that almost everyone said is working in so many previous posts puts time 4 hrs ahead with "$(TZ=$(date +%Z)+24 date +%Y%m%d%H%M)" and works with " echo $(TZ=$(date +%Z)+28 date +%Y%m%d%H%M)" syntax.
I personally wouldn't choose to modify the TZ variable in order to do date manipulation, because it's not so easy for others to understand your code in the future. However, you can do more background reading here: TZ Variable - The GNU C Library
# 10  
Old 04-21-2011
Even though "echo $(date +%Z)" is giving "EDT", using it to derive datetime is resulting a GMT datetime.

Code:
 
echo $(TZ=$(date +%Z)+24 date +%Y%m%d%H%M)


How can we correct above statement to give US Eastern Daylight savings aware datetime?

Following works as a stand alone.., but I could not substitute it with %Z and add +24 to it.

Code:
 
$> export TZ="America/New_York"; echo $(date +%TZ)


# 11  
Old 04-21-2011
That "+24" construct is not portable and that's why it's biting you. If you read that FAQ article, I point out the non-portability of this technique. But the idea that the authors of this technique were shooting for was to add 24 to the offset already used by the timezone software. It appears that you are overriding your value rather than modifying it. Rather than screwing around with this troublesome contruct, why not just use one the reasonable solutions that have been offered?
# 12  
Old 04-21-2011
wow, Looks like I am offending too many people here.. I will stop asking more questions on this topic.
# 13  
Old 04-21-2011
Regarding your offset, this may give you some ideas:
https://www.unix.com/shell-programmin...ate-hp-ux.html
or
https://www.unix.com/shell-programmin...n-solaris.html
This User Gave Thanks to ctsgnb For This Post:
kchinnam
# 14  
Old 04-21-2011
Thanks a lot ctsgnb, I will stop looking for a one liner solution for this using ksh/bash.
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