some changes

shell/Bash-Scripting.txt

@@ -402,8 +402,8 @@
 |   \       | Escape        |   hell\.o |   hell.o          |
 |           | character -   |           |   NOT:helllo,     |
 |           | escape any of |           |   hell1o...       |
-|           | the special   |           |                   |
-|           | character,    |           |                   |
+|           | the special   |           |   (Usefule with   |
+|           | character,    |           |    grep)          |
 |           | ignore the    |           |                   |
 |           | meaning of    |           |                   |
 |           | them          |           |                   |
@@ -660,3 +660,54 @@
         | read name     #richard                read name       #richard
         | hello Peter   #hello Peter            hello Peter     #hello Peter
         | echo $name    #Peter                  echo $name      #richard
+
+
+-> Comments:
+
+    * Single line:
+        use: #
+
+    * Multi-line:
+        use: : << cmt
+             This is
+             multiline Comments
+             in bash
+             cmt
+
+-> String in double quotes:
+
+    In double quotes the variable value is replaced
+    but the special character like * (wildcard)
+    character is not replaced.
+    
+    Special character is replaced when used without
+    double quotes and without double quotes use '\'
+    before it to supress the behaviour of special
+    characters.
+
+-> source keyword:
+
+    source keyword is used to run the shell script
+    in the same bash shell.
+
+    Since, running a shell scripts run the script
+    in seperate bash shell by default, running it
+    with source keyword run the script in same bash
+    shell.
+
+    Syntax:
+    source ./<script-name>
+
+-> := operator:
+
+    This operator only used to initialize uninitialized
+    variable with a value.
+
+    Syntax:
+
+    hh = 4;
+    hh := 5;
+    echo hh
+
+    Output:
+    4