#!/bin/ksh                                                              
# input format YYYY-MM-DD prints day name                               
dow()                                                                   
{                                                                       
 perl -e '                                                              
  use POSIX qw(strftime);                                               
  $fmt = "%A";  # %a = abbreviated weekday %u = weekday number          
  $mday = substr("$ARGV[0]", 8, 2);                                     
  $mon =  substr("$ARGV[0]", 5 ,2);                                     
  $year = substr("$ARGV[0]", 0 ,4);                                     
  $weekday =                                                            
    strftime($fmt, 0, 0, 0, $mday , $mon - 1, $year - 1900, -1, -1, -1);
  print "$weekday";                                                     
  ' "$1"                                                                
}                                                                       
for foo in -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 +6 +7 +8 +9 +10 +11
do
    FOO="FOO"${foo}
    export TZ=$FOO
    echo "TZ=${FOO}: `date`"
    echo "$(dow `date "+%Y-%m-%d"` )"                                       
done
echo '*****************  GMT -4'
export TZ=GMT-4
    echo "TZ=${TZ}: `date`"
    echo "$(dow `date "+%Y-%m-%d"` )"

dow()  
{
 export TZ=GMT-4
 perl -e '
  use POSIX qw(strftime);
  $fmt = "%A";  # %a = abbreviated weekday %u = weekday number 
  $mday = substr("$ARGV[0]", 8, 2);
  $mon =  substr("$ARGV[0]", 5 ,2);
  $year = substr("$ARGV[0]", 0 ,4);
  $weekday =
    strftime($fmt, 0, 0, 0, $mday , $mon - 1, $year - 1900, -1, -1, -1);
  print "$weekday";
  ' "$1"
}