c:\@Work\Perl>perl -wMstrict -le
"my $s = 'perlmonks IS a gREat site. dO you tHiNk SO? I loVE it!';
 print qq{'$s'};
 ;;
 my $senterm = '.?!';
 my $sentence = qr{ \b [[:alpha:]] [^\Q$senterm\E]* [\Q$senterm\E] }xms;
 ;;
 $s =~ s{ ($sentence) }{\u\L$1}xmsg;
 print qq{'$s'};
"
'perlmonks IS a gREat site. dO you tHiNk SO? I loVE it!'
'Perlmonks is a great site. Do you think so? I love it!'