UNIX for Dummies Questions & Answers

How would I go about getting the previous date on the server? I'm out of ideas...I am thinking that I could do it using the date command, but I am unable to find any information on doing it. For example if the current date is April 17th 2008 it would be (20080417) <- (YYYYMMDD). I need the previous date which is April 16th 2008 stored in the following format (20080416) <- (YYYYMMDD). I breifly thought that I could just subtract 1 from the day (DD) amount, but the only problem is what if it is the 1st of the month, I would then be unable to tell if it should be the 30th, 31st, or even the 29th? Please help. Thanks all

One way:

Code:

#!/bin/ksh

perl -e ' use POSIX qw(strftime); print strftime "%Y%m%d\n", localtime(time - 86400);  ' | read yest
echo $yest

Thanks for the quick reply, Do you know any other way that I could do it?...I was trying to find a way to do it without using perl?

If you have gnu date or install the gnu version of date it will do that.

If you care to install ksh93 instead of ksh88 it will do that.

The only other option is to write a fairly large piece of shell code.
Go to the FAQ - look for Perderabo's 'Date Arithmetic' thread. There are examples there.

Code:

#!/usr/bin/ksh
YESTURDAY=`TZ=EST+24 date +%Y%m%d`
echo $YESTURDAY

Note: if your timezone is something other than EST5DST just put in what your's is and it should work just fine. Some OS's you can change more than 1 day, HP-UX one day is as far as you can go with this approach.