$
$ # show the contents of the data file
$ cat -n f0
     1  RXOCF-8
     2
     3  CLASS 2A
     4  57
     5
     6  RU
     7  40
     8
     9  RXORX-8-0
    10
    11  CLASS 1B
    12   23 45 16
    13
    14  RXORX-8-1
    15
    16  EXTERNAL CLASS 2A
    17   6
    18
    19  RXOCF-21
    20
    21  RXOTX-34-1
    22
    23  CLASS 1B
    24   2
$
$
$ ##
$ perl -ne 's/^\s*//; s/\s*$//; chomp;
>           if (/./) {
>             if (/^RX/ and $x) {
>               print "$str\n";
>               $str = $_;
>             } elsif (/^RX/) {
>               $x = 1;
>               $str .= $_;
>             } elsif (/CLASS/) {
>               $prfx = "$_:";
>             } elsif ($prfx) {
>               @arr = split/ /;
>               $str .= " $prfx".join(" $prfx", @arr);
>               $prfx = "";
>             } else {
>               $str .= " $_";
>             }
>           }
>           END {print $str,"\n"}
>          ' f0
RXOCF-8 CLASS 2A:57 RU 40
RXORX-8-0 CLASS 1B:23 CLASS 1B:45 CLASS 1B:16
RXORX-8-1 EXTERNAL CLASS 2A:6
RXOCF-21
RXOTX-34-1 CLASS 1B:2
$
$

$
$ ##
$ perl -ne 's/^\s*//; s/\s*$//; chomp;
>           if (/./) {
>             if (/^RX/ and $x) {print "$str\n"; $str = $_}
>             elsif (/^RX/) {$x = 1; $str .= $_}
>             elsif (/CLASS/) {$prfx = "$_:"}
>             elsif ($prfx) {s/^|[ ]+/ $prfx/g; $str .= $_; $prfx=""}
>             else {$str .= " $_"}
>           } END {print $str,"\n"}' f0
RXOCF-8 CLASS 2A:57 RU 40
RXORX-8-0 CLASS 1B:23 CLASS 1B:45 CLASS 1B:16
RXORX-8-1 EXTERNAL CLASS 2A:6
RXOCF-21
RXOTX-34-1 CLASS 1B:2
$
$