See perlref and Modern Perl

Making References
References can be created in several ways.

1.  By using the backslash operator on a variable, subroutine, or valu
+e.
    (This works much like the & (address-of) operator in C.) This
    typically creates *another* reference to a variable, because there
+'s
    already a reference to the variable in the symbol table. But the
    symbol table reference might go away, and you'll still have the
    reference that the backslash returned. Here are some examples:

        $scalarref = \$foo;
        $arrayref  = \@ARGV;
        $hashref   = \%ENV;
        $coderef   = \&handler;
        $globref   = \*foo;
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