UNIX for Dummies Questions & Answers

Sometimes at the end of a long day, I can find STRANGE ways to solve otherwise simple questions. However, the following is an interesting approach.
The key is that you said you would cron (start) the task on the 1st of every month. Thus, I only need to find out yesterday.

Create a temp file, and determine the number of seconds since Epoch

Code:

> touch file163
> f163=`stat -c %Z file163`
> echo $f163
1233870219

Back off a day = 60 sec X 60 min X 24 hours
Find its time since Epoch

Code:

> f163a=`echo "$f163 - (60*60*24)" | bc`
> echo $f163a
1233783819

Find out the month for yesterday

Code:

> echo $(date '+%m' -d @$f163a)
02
> echo $(date '+%h' -d @$f163a)
Feb

And, to prove it out, since today is the 5th, I will back up 5 days
(voila, January!)

Code:

> f163b=`echo "$f163 - (5*60*60*24)" | bc`
> echo $f163b
1233438219
> echo $(date '+%m' -d @$f163b)
01
> echo $(date '+%h' -d @$f163b)
Jan