UNIX for Dummies Questions & Answers

Hello,
I'm new to shell scripting.
We've develop a script which will grep a file on the search criteria, MON (Jan/Feb/Mar/etc). But we should set this sript in cron which will run on every first day of the month. The problem I'm having is, when I run the script, it is displaying the contents of the present month. But I need the contents of the last month.
If the present month is Feb, the output that I should get is of Jan.
I'm using below in the script.
********************************************
set -x
#!/bin/sh
MON=`date +%b` #Feb
grep \/$MON\/ File1.txt > Output1.txt #This file should have the contents of Jan, not of Feb.
********************************************

Can anyone please help me to achieve the expecting output.

Thanks
~Suneel

IF your using gnu date:

Code:

date '+%b' --date '1 month ago'

Code:

#!/bin/ksh
 
# Setting an array from 0 to 11
set -A months Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov
 
j=`date +%m`           # current month
i=`expr $j - 1`           # substracting 1 
echo ${months[$i]}    # getting previous month from the array

To complete with your example

Code:

#!/bin/ksh
 
# Setting an array from 0 to 11
set -A months Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov
 
j=`date +%m`                # current month
i=`expr $j - 1`             # substracting 1 
MON=`echo ${months[$i]}`    # Assigning previous month to MON
grep \/$MON\/ File1.txt > Output1.txt 

If not using gnu date (as above) which I was not - you can simply do this:

MON=`TZ=CST+24 date +%b`

This assumes you are running within the first 24 hours of the 1st day of the month. You can adjust the 24 up accordingly if running later.

John

awesome solution, John.

I had always solved this type of problem with brute force.

Thanks all. The solution provided by John helped me a lot. As I need to add some more flavor to the original script, I can use neither GNU date nor ksh. But these solutions helped me for the records and also for my training purpose.
Once again thanks a lot all.
Cheers
~Suneel