Update bash.md

bash.md

@@ -1,4 +1,4 @@
-(---
+---
 title: Bash scripting
 category: CLI
 layout: 2017/sheet
@@ -211,9 +211,10 @@ echo ${STR^}   #=> "Hello world!" (uppercase 1st letter)
 echo ${STR^^}  #=> "HELLO WORLD!" (all uppercase)
 ```
 
-
 ### Default values
 
+| Expression        | Description                                              |
+| ----------------- | -------------------------------------------------------- |
 | `${FOO:-val}`     | `$FOO`, or `val` if unset (or null)                      |
 | `${FOO:=val}`     | Set `$FOO` to `val` if unset (or null)                   |
 | `${FOO:+val}`     | `val` if `$FOO` is set (and not null)                    |
@@ -221,7 +222,6 @@ echo ${STR^^}  #=> "HELLO WORLD!" (all uppercase)
 
 Omitting the `:` removes the (non)nullity checks, e.g. `${FOO-val}` expands to `val` if unset otherwise `$FOO`.
 
-
 Loops
 -----
 {: .-three-column}