perldoc -f my

   my VARLIST
    my TYPE VARLIST
    my VARLIST : ATTRS
    my TYPE VARLIST : ATTRS
            A "my" declares the listed variables to be local (lexically) to
            the enclosing block, file, or "eval". If more than one variable is
            listed, the list must be placed in parentheses.

            The exact semantics and interface of TYPE and ATTRS are still
            evolving. TYPE may be a bareword, a constant declared with "use
            constant", or "__PACKAGE__". It is currently bound to the use of
            the "fields" pragma, and attributes are handled using the
            "attributes" pragma, or starting from Perl 5.8.0 also via the
            "Attribute::Handlers" module. See "Private Variables via my()" in
            perlsub for details, and fields, attributes, and
            Attribute::Handlers.

            Note that with a parenthesised list, "undef" can be used as a
            dummy placeholder, for example to skip assignment of initial
            values:

                my ( undef, $min, $hour ) = localtime;