split slide on variable exapnsion in two

Bash.md

@@ -246,22 +246,29 @@ myvar=$( ls )
 
 ## String manipulation
 
-Consider `string=abcABC123ABCabc` and `filename=myfile.txt`
+Consider `string=abcABC123ABCabc`
 
 * string length : `${#string}` is `15`
 * substring extraction : 
   * `${string:7}` is `23ABCabc`
   * `${string:7:3}` is `23A`
   * `${string:(-4)}` or `${string: -4}` is `Cabc` 
-* substring removal from front :
-  * `${filename##myfile}` is `.txt`
-* substring removal from back :
-  * `${filename%%.txt}` is `myfile`
 
-<!--## Variable expansion
+---
+
+## String manipulation
+
+Consider `filename=/var/log/messages.tar.gz`
 
-* `${variable-default}` : 
-  if `variable` is unset or null, the expansion of `default` is substituted-->
+* substring removal from left :
+  * `${filename##/var}` is `/log/messages.tar.gz`
+* substring removal from right :
+  * `${filename%%.gz}` is `/var/log/messages.tar`
+
+You can use `*` to match all characters:
+
+* `${filename%%.*}` is `/var/log/messages`
+* `$(filename##*/)` is `messages.tar.gz`
 
 ---
 
@@ -269,7 +276,7 @@ Consider `string=abcABC123ABCabc` and `filename=myfile.txt`
 
 |  Operator    |     Operation   |
 | ------------ | --------------- |
-|  `+` `-` `\*` `/` |  addition, subtraction, multiply, divide |
+|  `+` `-` `\*` `/` |  addition, subtraction, multiplication, division |
 |  `var++` | increase the variable var by 1 |
 |  `var--`    |  decrease the variable var by 1 |
 |  `%`    |  modulus (remainder after division) |
@@ -309,7 +316,7 @@ a=$( expr 10 - 3 )
   > it is the **preferred method**
 -->
 ---
-
+# Arithmetic
 ```bash 
 #!/bin/bash
 
@@ -626,7 +633,7 @@ Try a simple example called `test_arg.sh` :
 echo $1 $2 $4
 echo $0
 echo $#
-echo $*
+echo $@
 ```
 
 ```bash