Returns an uppercased version of EXPR. If EXPR is omitted, uses $_.
my $str = uc("Perl is GREAT"); # "PERL IS GREAT"This function behaves the same way under various pragmas, such as in a locale, as lc does.
If you want titlecase mapping on initial letters see ucfirst instead.
Note: This is the internal function implementing the \U escape in double-quoted strings.
my $str = "Perl is \Ugreat\E"; # "Perl is GREAT"