To clarify:   the shell has its own way of handling “$whatever”:  it substitutes an environment-variable.   But if you are assembling a double-quoted string, and perhaps in other situations also, “Perl gets there first,” and substitutes a Perl variable (or nothing).   There are various ways to avoid this behavior, including the use of \$ (which means, “the literal character, ‘$’”).   Hence, I stand by the admonition to “first, just print it out.”   It is a (very easy!) waste of time to try to figure out why a string is not being interpreted correctly, only to discover (too late!) that the string does not actually contain what you thought it would.

(Let’s ask the Peanut Gallery here:    Will everyone who has done exactly this, please raise your hands?”   :-D   I rest my case.   (And lower my hand.)