i cant access unix so cant test this, but i think u can just write $1=$5 instead of
print $1=$5; and the print the first four after the inner block..

i dont quite understand the logic behind the line
if( key==$1 || key=="" ) {
and
key=$1;
but u wudve thot of smthing, anyway.. try it out

Or, and especially if this is a big file, import into a databse and use isnull