modify basic filestructure

It's unclear what's 'basic', so `basic/` notes have been mostly moved.
The remainder became `shell/`.

shell/ls.md

@@ -0,0 +1,46 @@
+---
+title: "ls"
+tags: [ "basics" ]
+---
+
+Firstly, your `ls` is probably aliased to something.
+
+Check it with:
+
+
+```sh
+alias ls
+```
+If the prompt shows some alias, then start by removing it:
+
+
+```sh
+unalias ls
+```
+
+Now we can begin.
+
+Check the most recently modified file:
+
+
+```sh
+ls -t
+```
+
+Reverse this with `tac` to see the file which has been unmodified the longest:
+
+
+```sh
+ls -t | tac
+```
+Group files by extension:
+
+```sh
+ls -X
+```
+Sort largest files first:
+
+```sh
+ls -X
+```
+