c:\@Work\Perl\monks>perl -wMstrict -le
"$_ = 'Three, Four, One, Two';
 ;;
 /([A-Z][a-z][.][\b])/;
 print qq{'$1'  '$2'  '$3'  '$4'};
 ;;
 /([A-Z] [a-z]+ (?: , | \b))/x;
 print qq{'$1'  '$2'  '$3'  '$4'};
"
Use of uninitialized value $1 in concatenation (.) or string at -e line 1.
Use of uninitialized value $2 in concatenation (.) or string at -e line 1.
Use of uninitialized value $3 in concatenation (.) or string at -e line 1.
Use of uninitialized value $4 in concatenation (.) or string at -e line 1.
''  ''  ''  ''
Use of uninitialized value $2 in concatenation (.) or string at -e line 1.
Use of uninitialized value $3 in concatenation (.) or string at -e line 1.
Use of uninitialized value $4 in concatenation (.) or string at -e line 1.
'Three,'  ''  ''  ''

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'foo bar baz';
 $s =~ m{ (foo) \s* (bar) \s* (baz) }xms;
 print qq{A:  '$1'  '$2'  '$3'};
 ;;
 $s =~ m{ (xyzzy) }xms;
 print qq{B:  '$1'  '$2'  '$3'};
 ;;
 $s =~ m{ (b \w*) }xms;
 print qq{C:  '$1'  '$2'  '$3'};
"
A:  'foo'  'bar'  'baz'
B:  'foo'  'bar'  'baz'
Use of uninitialized value $2 in concatenation (.) or string at -e line 1.
Use of uninitialized value $3 in concatenation (.) or string at -e line 1.
C:  'bar'  ''  ''

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'Three, Four, One, Two, xFive9';
 print qq{'$s'};
 ;;
 my @numbers = $s =~ m{ \b [[:upper:]] [[:lower:]]+ \b }xmsg;
 printf qq{'$_' } for @numbers;
 print '';
 ;;
 my %correct;
 @correct{ @numbers } = qw(one two three four);
 ;;
 my ($rx_search) =
   map  qr{ \b (?: $_) \b }xms,
   join '|',
   map  quotemeta,
   keys %correct
   ;
 print $rx_search;
 ;;
 $s =~ s{ ($rx_search) }{$correct{$1}}xmsg;
 print qq{'$s'};
"
'Three, Four, One, Two, xFive9'
'Three' 'Four' 'One' 'Two'
(?^msx: \b (?: Four|Three|Two|One) \b )
'one, two, three, four, xFive9'