#!/ur/bin/ksh

# Usage : GetDate nDays [format]
# Examples :
#    echo "Yesterday: $(GetDate -1)"
#    echo "Tomorrow: $(GetDate 1)"
#    echo "Next week: $(GetDate 7 '+%Y-%m-%d')"

GetDate(){
  typeset -i nDays=$1; format=$2
  typeset -i localOffset=$(echo $TZ |
   sed 's![^-0-9]*\([-0-9]*\).*!\1!')
  TZ=X$((localOffset-24*nDays)) date $format
}

awk '
function timestamp(date, hour, ampm    ,d,h) {
   split(date,d,"/");
   split(hour,h,":");
   if ( tolower(ampm) == "pm") h[1] += 12;
   return sprintf("%04d%02d%02d%02d%02d%02d",d[3],d[1],d[2],h[1],h[2],h[3]);
}
timestamp($1,$2,$3) >= limit
' limit=$(GetDate -1 '+%Y%m%d%H%M%S')  input_file

#!/usr/bin/awk -f

function isleapyear(year) {
   return ( year % 4 == 0 && (year % 100 != 0 || year % 400 == 0))
}

function yesterday_timestamp(   date_cmde) {
   date_cmde = "date +'%Y %m %d %H%M%S'";
   date_cmde | getline;
   close(date_cmde);
   if (--$3 == 0) {
      if (--$2 == 0) {
         $2 = 12;
         $1 -= $1;
      }
      $3 = substr("00312831303130313130313031",$2*2+1,2);
      if ($2 == 2 && isleapyear($1)) $2 = 29;
   }
   return sprintf("%04d%02d%02d%06d",$1,$2,$3,$4)
}
function timestamp(date, hour, ampm    ,d,h) {
   split(date,d,"/");
   split(hour,h,":");
   if ( tolower(ampm) == "pm") h[1] += 12;
   return sprintf("%04d%02d%02d%02d%02d%02d",d[3],d[1],d[2],h[1],h[2],h[3]);
}

BEGIN {   limit = yesterday_timestamp() }

timestamp($1,$2,$3) >= limit
' input_file