change ``bash headers to ``sh

basics/ls.md

@@ -8,13 +8,13 @@ Firstly, your `ls` is probably aliased to something.
 Check it with:
 
 
-```bash
+```sh
 alias ls
 ```
 If the prompt shows some alias, then start by removing it:
 
 
-```bash
+```sh
 unalias ls
 ```
 
@@ -23,24 +23,24 @@ Now we can begin.
 Check the most recently modified file:
 
 
-```bash
+```sh
 ls -t
 ```
 
 Reverse this with `tac` to see the file which has been unmodified the longest:
 
 
-```bash
+```sh
 ls -t | tac
 ```
 Group files by extension:
 
-```bash
+```sh
 ls -X
 ```
 Sort largest files first:
 
-```bash
+```sh
 ls -X
 ```