[avar]

Some of it you pickup or remember from the context of the file you're looking at, but you really should take the time to read the manuals for these tools from cover to cover at some point if you're making extensive use of them. In the case of GNU bash & make: https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.... & https://www.gnu.org/software/make/manual/make.html