open(FH, "+<", "$filename") or die "Opening: $!";
@ARRAY = <FH>;
# change ARRAY here
seek(FH,0,0) or die "Seeking: $!";

    for($i=0;$i<=$#ARRAY;$i++)
    {
        $line = $ARRAY[$i];
        $line=~s#find#replace#;
        $ARRAY[$i] = $line;
    }

print FH @ARRAY or die "Printing: $!";
truncate(FH,tell(FH)) or die "Truncating: $!";
close(FH);