Débutante en SCRIPT SELL Les opérateurs boolé

#!/bin/ksh 
echo ' '>test.ls 
event_start_date_4=0 
cat ict_detail_20120604_20120605.dat | while read ligne 
do 
 event_start_date_='echo $ligne|awk -F";" '{print $7}'' 

  
 if ! [ -d $event_start_date_ ] 
  then 
   echo $event_start_date_ 
   event_start_date_1='echo $event_start_date_|awk -F"/" '{print $1}'' 
   event_start_date_2='echo $event_start_date_|awk -F"/" '{print $2}'' 
   event_start_date_3='echo $event_start_date_|awk -F"/" '{print $3}'' 
   event_start_date_4='echo $event_start_date_3$event_start_date_2$event_start_date_1' 
   echo $event_start_date_4 
  if  $event_start_date_4 >= 20001010  &&  $event_start_date_4 <= 20201010  
  then 
  echo $event_start_date_4>>test.ls 
  fi 
 fi 
done 

test2_2.shh[18]: 20120604:  not found