Perl's uc() function takes a string, makes the entire thing uppercase, and then returns the new string.
$STRING = uc($STRING);
First, $myWord is set to a value of 'word', then the uc() function is run on $myWord. The uc() function takes the entire string $myWord and converts it to it's uppercase equivalent. The value of $myUpperWord is then equal to 'WORD'.
$myWord = 'word'; $myUpperWord = uc($myWord);