Shell Programming and Scripting

#!/bin/ksh
today=`date +%Y%m%d`
TRAILER=false
HEADER=false
DETAIL=0
while read LINE
do
#
#  Validating 1st record is Header + header's date
#
   FIRST_CAR=`echo $LINE | cut -c1`
   if [ $HEADER = "false" -a $FIRST_CAR = "H" ]
   then
      HEADER=true
      echo $LINE | grep $today > /dev/null
      if [ $? -eq 1 ]
         echo "Header record not from today"
         exit 1
      fi
   else
#
#  Validating detail record or trailer recors
#
      if [ $HEADER = "true" ]
      then
         if [ $FIRST_CAR = "D" ]
         then
            if [ $TRAILER = "false" ]
            then
               DETAIL=`expr $DETAIL + 1`
            else
               echo "File is corrupt - Detail record found after a trailer record"
               exit 1
            fi
         else
            if [ $FIRST_CAR = "T" -a $TRAILER = "false" ]
            then
               TRAILER=true
               TOT=`echo $LINE | cut -c2-`
               if [ $DETAIL -ne $TOT ]
               then
                  echo "File is corrupt - Number of detail record mismatch"
                  exit 1
               fi
            else
               echo "File is corrupt - Invalid record or more than one header/trailer record"
               exit 1
            fi
         fi
      else
          echo "File is corrupt - No header record found"
          exit 1
      fi
   fi
done < $1
if [ "$TRAILER" = "false" ]
then
   echo "File is corrupt - No trailer record found"
   exit 1
else
   echo "File seems to be Ok"
fi

 TOT=${LINE#?}