How do I calculate the previous business day in ksh shell script?

Question

What is the most elegant way to calculate the previous business day in shell ksh script ?

What I got until now is :

#!/bin/ksh

set -x

DAY_DIFF=1
case `date '+%a'` in
"Sun")
   DAY_DIFF=2
   ;;
"Mon")
   DAY_DIFF=3
   ;;
esac

PREV_DT=`perl -e '($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst)=localtime(time()-${DAY_DIFF}*24*60*60);printf "%4d%02d%02d",$year+1900,$mon+1,$mday;'`

echo $PREV_DT

How do I make the ${DAY_DIFF} variable to be transmitted as value and not as string ?

Solution

Here is a solution that doesn't use Perl. It works both with ksh and sh.

#!/bin/ksh

diff=-1
[ `date +%u` == 1 ] && diff=-3

seconds=$((`date +%s` + $diff * 24 * 3600))
format=+%Y-%m-%d

if date --help 2>/dev/null | grep -q -- -d ; then
    # GNU date (e.g., Linux)
    date -d "1970-01-01 00:00 UTC + $seconds seconds" $format
else
    # For BSD date (e.g., Mac OS X)
    date -r $seconds $format
fi

Comments

[jwg]

'Business day' is a standard term which never includes Sat and Sun.