Solaris

#!/bin/bash
# epoch.sh
# Usage: ./epoch.sh YYYYMMDD
EPOCH=$1
if [ "$EPOCH" == "" ]
then
	exit 1
fi
echo '#epoch.py
import time
mydate='\"$EPOCH\"'
epoch=int(time.mktime(time.strptime(mydate, "%Y%m%d")))
print(time.strftime("%A", time.localtime(epoch)))
exit()' > "$HOME"/epoch.py
DAY=$( python "$HOME"/epoch.py )
echo "$DAY"

Last login: Tue Mar 27 22:13:36 on ttys000
AMIGA:amiga~> cd Desktop/Code/Shell
AMIGA:amiga~/Desktop/Code/Shell> ./epoch.sh 20180327
Tuesday
AMIGA:amiga~/Desktop/Code/Shell> ./epoch.sh 20180328
Wednesday
AMIGA:amiga~/Desktop/Code/Shell> _

#!/bin/bash

zeller() {
   year=$1 month=$2 day=$3
   (( 10#$month < 3 )) && year=$(( year - 1 ))
   F=$(( (10#$day + ((13 * ((10#$month+9) % 12) + 12)/5) + \
                (5*(year%100))/4 + (year/400) - 2*(year/100))%7 ))
   (( F<0 )) && (( F = F + 7 ))
   echo $F
}

for date in $@
do
   y=${date:0:4} m=${date:4:2} d=${date:6:2}
   dow=$(zeller $y $m $d)
   if (( dow == 3 ))
   then 
      printf "%02d/%02d/%4d (%s) is a Wednesday\n" $d $m $y $date
      # US date format: (comment above and uncomment below if in the USA)
      #printf "%20d/%02d/%4d (%s) is a Wednesday\n" $m $d $y $date
   else
      printf "%02d/%02d/%4d (%s) is NOT a Wednesday\n" $d $m $y $date
      # US date format:
      #printf "%02d/%02d/%4d (%s) is NOT a Wednesday\n" $m $d $y $date
   fi
done

$ zeller.sh 2017 3 25
6
$ zeller.sh 2017 3 1
3