UNIX for Dummies Questions & Answers

Hello,
I could not find the exactly same post here.. so I will explain what I did to get the last month using date command.

I used

Code:

date +%Y-%m -d "-1 months"

to get the last month. However, the returned value of above command on 2009/10/31 was 2009 10 and not 2009 09.. and the returned value on 2009/12/31 was 2009 12 and not 2009 11.
When I tried it on 2010/01/31, it returned 2009 12, which is what I wanted.
So it seems if I try this command on 31 and if the previous month does not have 31, it fails to return the correct value..
This logic leads to me that it will also fail when I try it on 2010/03/29, 30, 31 because there is no 2010/02/29, 30, 31...
Is it how date command works?? What do I have to do to get the correct 'Last month' even on 31...

I really appreciate your help!

Which Operating System do you have?

I have Redhat ES 4.5

You can try fooling the system by pretending that it is always mid-month (untested).

Code:

date -d "$(date +%Y-%m-15) -1 month"

see the following date command examples

Code:

date -d "1 month ago"

using this we can manipulating the date.

see the following more examples.

The following example used for current date from ago

Code:

#date
Tue Feb 23 14:32:14 IST 2010

#date -d "1 day ago"
Mon Feb 22 14:32:18 IST 2010

#date -d "1 week ago"
Tue Feb 16 14:32:24 IST 2010

#date -d "1 month ago"
Sat Jan 23 14:32:29 IST 2010

 #date -d "1 year ago"
Mon Feb 23 14:32:35 IST 2009

The following example used for current date after

Code:

  #date
Tue Feb 23 14:35:00 IST 2010

#date -d "+1 day"
Wed Feb 24 14:35:05 IST 2010

#date -d "+1 week"
Tue Mar  2 14:35:09 IST 2010

#date -d "+1 month"
Tue Mar 23 14:35:14 IST 2010

#date -d "+1 year"
Wed Feb 23 14:35:21 IST 2011

@ungalnanban

The o/p highlights the fact that his date command does not work if today's day number did not exist in the previous month.
e.g. 31/03/10 is a valid date but 31/02/10 is not. The o/s in use translates 31/02/10 into 03/03/10 ! Because the o/p wanted the previous month number it is wrong.
My circumvention is to fool "date" that is mid-month but I can't test the syntax without having a copy of Redhat.

Can you try it on your test system and post the results.

That is what I had... when I execute that command on Dec/31/2009, it returns Dec/01/2009 not Nov/30/2009... I changed the system date to March/29, 30, 31 and tried that command... it returned March 1, 2, 3... It also does not work for next month on those days..
So...I guess this is the spec of date command...