Shell Programming and Scripting

Ok, the title is confusing i know, but it is a weird question.

I have a bash script running on Centos5.8 and want to find a better way to do some date manipulation. What i am trying to do is get 3 days of files (day before, that day, and day after), concatenate the three files and pass them on to the next script. This is easy for days in the same month but if i'm pulling for the first of the month i have to figure out what was the last day of the previous month was. I also have to check each time to see if the target date is the last day of that month. Currently i subtract 1 from the month and do a cal command with it and the year (not even dealing with jan 1 yet), strip out the text and count the remaining to get number of days. I would be so much easier if i could just get previous day and following day of $Target_date. I know i can do it on todays date i just can't find a way to specify the date to manipulate.

You have Linux, so probably have GNU Date, which can do easy date math.

Code:

$ date -d '2012/11/01 - 3 days' +%Y/%m/%d
2012/10/29

$

Thanks, i had tried a lot of patterns but never tried the

Code:

 '2012/11/01 - 3 days'

in the mix.