Adds Indirection and prefix name expansion (#2102)

bash.md

@@ -173,7 +173,7 @@ echo "${str/foo/bar}" # /path/to/bar.cpp
 
 ```bash
 str="Hello world"
-echo "${str:6:5}" # "world"
+echo "${str:6:5}"  # "world"
 echo "${str: -5:5}" # "world"
 ```
 
@@ -183,6 +183,24 @@ base=${src##*/} #=> "foo.cpp" (basepath)
 dir=${src%$base} #=> "/path/to/" (dirpath)
 ```
 
+### Prefix name expansion
+
+```bash
+prefix_a=one
+prefix_b=two
+echo ${!prefix_*} # all variables names starting with `prefix_`
+prefix_a prefix_b
+```
+
+### Indirection
+
+```bash
+name=joe
+pointer=name
+echo ${!pointer}
+joe
+```
+
 ### Substitution
 
 | Code | Description |