nawk '
    {
	input=$0
	while(match(input,"%[0-9a-zA-Z][0-9a-zA-Z]")) {
	    str = substr(input,RSTART+1,RLENGTH-1)
	    val = hex2char(str)
	    sub("%[0-9a-zA-Z][0-9a-zA-Z]",val,input)
	}
	print input
    }
    function hex2char(s) {
	retval=0
	for(i=1; i<=length(s); i++) {
	    char=toupper(substr(s,i,1))
	    retval = 16*retval+match("0123456789ABCDEF",char)-1
	}
	return sprintf("%c",retval)
    }
'