Regex - capture optional surrounding characters

I'm not that savvy in regex, so I'm not sure how to achieve the following thing:

I'd like to capture any arbitary string from an input that may or may not be surrounded by the '$' character. If a '$' character is present at the beginning of the string, the '$' character at the end must be present.

Currently I have

^\w+([_.-]\w+)*$

which roughly translates to:

1. Arbitary word characters


2. Beginning of capture group


3. any character of '_', '.', '-'


4. Before an optional \n

So valid matches would be:

test
test-5
test.1.3
test-alpha.2

Now I'd like to make this possible

$test$

But not...

$test (or test$)