[google-search] How can I use a search engine to search for special characters?

Unfortunately, there doesn't appear to be a magic bullet. Bottom line up front: "context".

Google indeed ignores most punctuation, with the following exceptions:

1. Punctuation in popular terms that have particular meanings, like [ C++ ] or [ C# ] (both are names of programming languages), are not ignored.
2. The dollar sign ($) is used to indicate prices. [ nikon 400 ] and [ nikon $400 ] will give different results.
3. The hyphen - is sometimes used as a signal that the two words around it are very strongly connected. (Unless there is no space after the - and a space before it, in which case it is a negative sign.)
4. The underscore symbol _ is not ignored when it connects two words, e.g. [ quick_sort ].

As such, it is not well suited for these types of searchs. Google Code however does have syntax for searching through their code projects, that includes a robust language/syntax for dealing with "special characters". If looking at someone else's code could help solve a problem, this may be an option.

Unfortunately, this is not a limitation unique to google. You may find that your best successes hinge on providing as much 'context' to the problem as possible. If you are searching to find what $- means, providing information about the problem's domain may yield good results.

For example, searching "special perl variables" quickly yields your answer in the first entry on the results page.