Added documentation for '$variable' in scripting folder

_commands/scripting/$variable.md

@@ -0,0 +1,37 @@
+---
+---
+
+$ (Dollar sign prefix to a variable)
+-------
+
+'$variable'
+The prefix '$' lets the shell interpret 'variable' as a variable.
+
+~~~ bash
+$ echo $PATH
+/home/username/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/mnt/c/Program Files (x86)
+~~~
+
+<!--more-->
+
+### Useful Options / Examples
+
+#### 'MY_VAR="10"; echo $MY_VAR'
+~~~ bash
+$ MY_VAR=10; echo $MY_VAR
+10
+~~~
+
+
+##### Break it down
+* MY_VAR has value 10, and '$' must be used to print this value.
+
+#### 'EXEC="./correct.out"; $EXEC'
+~~~bash
+$ EXEC="./correct.out"; $EXEC
+correct output
+~~~
+
+##### Break it down
+
+* The terminal replaces the $EXEC with its value, and reads it as if it was typed by the user. Therefore, the terminal runs the executable 'correct.out'.