>perl -wMstrict -le
"my $chr;
 $chr = \"x this and that y\";
 $chr =~ s/(this|that)|(\w+)/\u$1\E$2/g;
 print \"$chr\n\";
"
Use of uninitialized value in concatenation (.) or string ...
Use of uninitialized value in concatenation (.) or string ...
x This and That y