>perl -wMstrict -le
"my $line =
   'CLASS A SOLD ON 17/11/10 FOR SETTLEMENT ON 22/11/10 @ 145.59993';
 ;;
 my $date = qr{ \d\d / \d\d / \d\d }xms;
 ;;
 my ($tdate) = $line =~
   m{ (?: PURCHASED | SOLD) \s+ ON \s+ ($date) }xmsg;
 print qq{tdate: '$tdate'};
 ;;
 my ($sdate) = $line =~ m{ SETTLEMENT \s+ ON \s+ ($date) }xmsg;
 print qq{sdate: '$sdate'};
"
tdate: '17/11/10'
sdate: '22/11/10'

##</code><code>##

>perl -wMstrict -le
"use Data::Dumper;
 ;;
 my $date = qr{ \d\d / \d\d / \d\d }xms;
 my $sep  = qr{ \s+ ON \s+         }xms;
 my @ops  = qw(PURCHASED SOLD SETTLEMENT);
 my $op   = join '|', map quotemeta, @ops;
    $op   = qr{ $op }xms;
 ;;
 READ_LOOP: {
 ;;
 my $line =
   'CLASS A SOLD ON 17/11/10 FOR SETTLEMENT ON 22/11/10 @ 145.59993';
 ;;
 next READ_LOOP
   if not my %dates = $line =~ m{ ($op) $sep ($date) }xmsg;
 print Dumper \%dates;
 ;;
 }
"
$VAR1 = {
          'SETTLEMENT' => '22/11/10',
          'SOLD' => '17/11/10'
        };