bash question?
 

I have a question about bash syntax. I am using something out of the gentoo install guide as an example

the line CXXFLAGS is supposed to have the same cflags as the above line, so why would it not be like this
what purpose do the brackets serve?

In the case of the example given, they are optional. There are many constructions where they are required, to mention just one:

${parameter:-word}

If you want the whole story: man bash, specifically the Parameter Expansion section.

On a personal note: I always use the brackets. I could be wrong, but I believe that's the way 'it's supposed to be done'.

Hope this helps.