date X months ago

[Alex Lavrov]

Hello!

Just wanted to ask, not to invent the wheel again, what is the *shortest* way in shell script to get date X months ago?
If today is 2003/09/21, I want to get 2003/06/21?

thanx!

[Steven E. Protter · Accepted solution]

This script will work.

It is the prior version of a great script from A. Clay Stephenson.

More current versions available on merijn's site which I have not bookmarked.

SEP

[john korterman]

Hi,


It could be my browser, but the famous caljd.sh posted by Stephen Protter is unreadable over here. However, it should be the easiest thing to search for in this forum.
caljd.sh accepts various parameters for e.g. asking for the date 90 days ago, as in this example:
# PREV90=$(caljd.sh -y -s $(caljd.sh -p 90))
# echo $PREV90
20030623

but I dont think that you can supply a number of months as parameter. If months ago is 2 and today is 2003/04/30. What would then be the correct answer?

regards,
John K.

[Rajeev Shukla]

Hi Alex,

Here is a simple C program i wrote to get date say X days back. It can be modified to get date in the desired format and needs a input variable as day.
Say you want to get date 3 days back you run it as
a.out 3
(a.out is the compiled program)
#include
#include
#include
#include
#include
int tm, day, tm1;
char *date, *dat;
main(argc, argv)
int argc;
char *argv[];
{
time(&tm);
day=atoi(argv[1]);
day=(day*24*60*60);
date = ctime(&tm);
printf("The Present Date & Time is : %s", date);
tm1=(tm - day);
dat = ctime(&tm1);
printf("The Date & Time %s days Back was: %s", argv[1],dat);
}

Cheers
Rajeev

[Stuart Browne]

If all else fails there's always GNU's date, which allows you to pass it plain-english strings for periods of difference:

gnu_date -d "3 months ago"

[A. Clay Stephenson]

What you are asking requires a bit more thought. It's rather easy to do ninety days ago but 3 months ago, even with Gnu date, is somewhat ambiguous. Consider the case of 3 months prior to 30-May-2003; that would naturally be 30-Feb-2003, right? You need to define the rules a bit better and then a good answer can emerge.