SUMMARY: ksh math

From: Cohen, Andy (Andy.Cohen_at_cognex.com)
Date: 06/30/04 

Date: Wed, 30 Jun 2004 16:29:07 -0400
To: "Tru64-Unix-Managers (E-mail)" <tru64-unix-managers@ornl.gov>

A fairly simple solution - one that I thought I had tried but obviously not.

This is what I chose to use:

        export PREV_RUN_DATE=$(( $RUN_DATE - 1 ))

This also worked:

        let PREV_RUN_DATE=$RUN_DATE-1

Thanks to Charlie Ballowe, Bob Sloane, Mark Scarborough, and Dr. Tom Blinn

ORIGINAL QUESTION
=================
I don't know what I'm missing -- all I want to do is do some very basic math on a variable but I can't figure it out. I've searched the archives, google, manuals, etc. and can't find anything that clarifies it.

I have a variable $RUN_DAY and I want to subtract one (1) from it. How do I do that?

I thought it would be:

    export PREV_DAY=${RUN_DAY}-1

but it doesn't work. I've tried quite a number of variations on this all to no avail.

I'm using:
    Tru64 5.1A
    korn shell (ksh)

Thank you!
Andy Cohen
Database Systems Administrator
Cognex Corporation
1 Vision Drive
Natick, MA 01760
508-650-3079