For example, I can run ln, nano, and programs I installed over apt like sl or worms without having to give the full path. However, when I build a program/package/software manually/using make/using something else, I have to invoke it using the full path, in my case ~/ghc/bin/ghc. How do you tell bash, or for that matter, sh, which names exist?
I know how to do this on Windows, but as far as I know, there's no equivalent of %PATH% in Linux/Unix/Ubuntu (in my case).