Need variable for yesterday's date

stefaandk · 01-28-2007, 08:34 PM

It's in a script that I didnt't write but this one specifies the date added to a backup filename

date=`/bin/date "+%Y%m%d"`

Now I need another variable that instead of today's date does the same thing but shows me yesterday's date.

I also have a Perl script that does show today's date

#!/usr/bin/perl
my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);
$s = sprintf("%02d%02d%02d", $mday, $mon+1, $year - 100);
print $s . "\n";

I can use either, I just need to get yesterday's date, so how would I adjust this?

Thanks

matthewg42 · 01-28-2007, 08:49 PM

You can do it nicely with a Perl one-liner:

Code:

#!/bin/bash

today=$(perl -e 'use Date::Format; $d = time(); print time2str("%Y-%m-%d\n", $d);')
yesterday=$(perl -e 'use Date::Format; $d = time() - (3600*24); print time2str("%Y-%m-%d\n", $d);')

echo "today is $today"
echo "yesterday was $yesterday"

Although you need to make sure you have the Date::Format module installed. In Ubuntu (Edgy), Date:Format is provided by the libtimedate-perl package.

matthewg42 · 01-28-2007, 08:54 PM

Oh, one more thing, the format strings for time2str are the same as those described in the strftime manual page.

Personally, I find that there are certain types of feature which are difficult to write in shell scripts and that cause me to switch my language up to a more sophisticated one like Perl. Any sort of detailed date calculations is one of those, as well as things which ae best implemented using associative arrays (hashes in Perl) or which need complex data structures..

Shell is nice, but it's a bit limited.

wjevans_7d1@yahoo.co · 01-28-2007, 10:08 PM

I did a quick google of

perl date

and came up with:

http://www.stonehenge.com/merlyn/UnixReview/col25.html

This should give you what you need. Hope it helps.

stefaandk · 01-28-2007, 10:13 PM

Thanks that should get me going.

yum install perl-time* on redhat for the package btw.

Cheers

Dark_Helmet · 01-28-2007, 10:49 PM

No need to go with perl. You can accomplish the same thing with the date command itself, and a bit more clearly as well:

Code:

yesterday_variable=`/bin/date -d '1 day ago'`

I'm not on my box to test right now, but I'm sure you could substitute 'yesterday', 'today - 1 day', 'today - 24 hours', etc. for the original date string.

The date man page gives examples of pre- and post-date date strings.

stefaandk · 01-28-2007, 11:06 PM

That works too and is nice and ez however, I need it to be in this format

29-01-2007

As I'm appending to a filename.

Cheers.

Dark_Helmet · 01-28-2007, 11:37 PM

The date command gives that flexibility too. From the date man page, just use the format specifier. The command becomes:

Code:

yesterday_variable=`/bin/date -d '1 day ago' '+%d-%m-%Y'`

Again, since I'm not on my box at home, I can't test that command. You may have to tweak it a little bit if it doesn't work out-of-the-box. See the date man page for help if you need to modify it.

matthewg42 · 01-28-2007, 11:50 PM

Far out, I didn't know about the -d option to date. Wonderful. Good to find a useful new option to a familiar tool.