Sometimes directory structures are a bit of a nest. You often want to see the full structure, but may not have access to packages like 'tree'. I found a great expression and decided to wrap it into an aliased command in ~/.bash_profile
alias tree="ls -R | grep \":$\" | sed -e 's/:$//' -e 's/[^-][^\/]*\//--/g' -e 's/^/ /' -e 's/-/|/'"
Now, when you want to see a complex directory structure in the shell, just change to the working directory, and type `tree`