Literal Values
Scalar Values
    ...
    ...
    String
        'abc'
            Literal string, no variable interpolation...except...
        "abc"
            A string in which variables are interpolated...
        `command`
            Evaluates to the output of the command.
        Class::
            A value that is mostly equivalent to "Class".
        1.2.3    v.5.6.0.1
            A string ("v-string") composed of the specified ordinals. ...
        <<identifier
            Shell-style "here document."
        __FILE__
            The name of the program file.
        __PACKAGE__
            The name of the current package.