C:\test>p1
$s = 'This is a string (with a bit in the middle) before the string ends';;
$r = \substr $s, 18, 24;;

print $$r;;
with a bit in the middle

$$r =~ s[([a-z]+)][\U$1]g;;

print $s;;
This is a string (WITH A BIT IN THE MIDDLE) before the string ends