Need to go back 1 day using the date command - UNIX for Dummies Questions & Answers

cfoxwell · #1 09-28-2001

I am trying to write a shell script to look at log files with dates in the file name.

Now I know how to use the expr command to subtract 1 day from the other, which is simple when the dates are from the 2nd to the 31st of each month.

But the problem I have is when the date turns to the 1st and the last month is 31st or 30th - because 1 -1 = -1 don't it, rather than 30 or 31

How do I write a script to handle this.

P.S I'm using KSH

LivinFree · #2 09-28-2001

Please search the forums, this has been brought up a few times today alone... Here are a few I found in a minute of searching:

Date Substraction

Date function question < -- That one has a few different ways of doing it...

98_1LE · #3 09-28-2001

This script was posted here some time ago, and I modified it slightly.

Code:

#!/usr/bin/ksh
date '+%m %d %Y' | 
{ 
read MONTH DAY YEAR
DAY=`expr "$DAY" - 1` 
case "$DAY" in 
        0) 
           MONTH=`expr "$MONTH" - 1` 
                case "$MONTH" in 
                        0) 
                           MONTH=12 
                           YEAR=`expr "$YEAR" - 1` 
                        ;; 
                esac 
        DAY=`cal $MONTH $YEAR | grep . | fmt -1 | tail -1` 
esac 
echo "Yesterday was: $MONTH $DAY $YEAR" 
}

Cameron · #4 12-06-2001

Ok, I understand the script and provided the following result ...
Yeseterday was: 6 12 2001 .

But how does one convert the month (12) into either the long or short name(ie - December/Dec).

I need to do this as Directories are named ... (eg - Nov2001, Dec2001, etc.). I'm trying to create a reporting script to run via cron on the 1st of every month perusing the pervious months sar files for system reports. The scripts purpose is to be run from cron and the command line if required (for reruns for eg.).

Any help appreciated - have already done a search.
Such is the life of a newbie.

Cameron · #5 12-11-2001

Try the following ...

## Long Name Month Listing.
lngmth="January February March April May June \
July August September October November December"
## Short Name Month Listing.
shtmth="Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec"

##
## Get Current Month Number (01-12).
xcurmth=`date +%m`
## Get Previous Month Number (01-11).
xprvmth=`expr $xcurmth - 1`
## Get Year Number (??).
xcuryr=`date +%Y`
## Get Previous Year Number (??).
xprvyr=`expr $xcuryr - 1`

xx=`echo $shtmth | cut -f$2 -d" "`
zz=`echo $lngmth | cut -f$2 -d" "`
XX=`echo $shtmth | cut -f$2 -d" "`$xprvyr
ZZ=`echo $lngmth | cut -f$2 -d" "`$xcuryr

If $xprvmth = 0 then you must use $xprvyr and 12 for the month. ...
(eg. `echo $shtmth | cut -f12 -d" "`$xprvyr)

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