Q&A : VB Scripting


Greetings!!

As you aware the knowledge in Vbscripting is very essential for a repackaging engineer.It will help for developing custom actions,Developing some process automation scripts etc..

The below Q&A I have prepared mainly for the newbies in Vbscripting.Hope this will be helpful for you.

What is VBScript?

  • VBScript is a scripting language
  • A scripting language is a lightweight programming language
  • VBScript is a light version of Microsoft’s programming language Visual Basic

What is a Variable?

A variable is a “container” for information you want to store. A variable’s value can change during the script. You can refer to a variable by name to see its value or to change its value. In VBScript, all variables are of type variant, that can store different types of data. 

What are the Rules for Variable Names?

  • Must begin with a letter 
  • Cannot contain a period (.)
  • Cannot exceed 255 characters

How to Declare Variables?

You can declare variables with the Dim, Public or the Private statement. Like this: 

dim name
name=some value

Now you have created a variable. The name of the variable is “name”.

You can also declare variables by using its name in your script. Like this:

name=some value

Now you have also created a variable. The name of the variable is “name”.

However, the last method is not a good practice, because you can misspell the variable name later in your script, and that can cause strange results when your script is running. This is because when you misspell for example the “name” variable to “nime” the script will automatically create a new variable called “nime”.  To prevent your script from doing this you can use the Option Explicit statement. When you use this statement you will have to declare all your variables with the dim, public or private statement. Put the Option Explicit statement on the top of your script. Like this:

option explicit
dim name
name=some value

 

How to Assign Values to Variables?

You can assign a value to a variable like this:

name="Hege"
i=200

The variable name is on the left side of the expression and the value you want to assign to the variable is on the right. Now the variable “name” has the value “Hege”.

What is Lifetime of Variables ?

How long a variable exists is its lifetime.

When you declare a variable within a procedure, the variable can only be accessed within that procedure. When the procedure exits, the variable is destroyed. These variables are called local variables. You can have local variables with the same name in different procedures, because each is recognized only by the procedure in which it is declared.

If you declare a variable outside a procedure, all the procedures on your page can access it. The lifetime of these variables starts when they are declared, and ends when the page is closed.

What are Array Variables ?

Sometimes you want to assign more than one value to a single variable. Then you can create a variable that can contain a series of values. This is called an array variable. The declaration of an array variable uses parentheses ( ) following the variable name. In the following example, an array containing 3 elements is declared:

dim names(2)

The number shown in the parentheses is 2. We start at zero so this array contains 3 elements. This is a fixed-size array. You assign data to each of the elements of the array like this:

names(0)="Tove"
names(1)="Jani"
names(2)="Stale"

Similarly, the data can be retrieved from any element using the index of the particular array element you want. Like this:

mother=names(0)

You can have up to 60 dimensions in an array. Multiple dimensions are declared by separating the numbers in the parentheses with commas. Here we have a two-dimensional array consisting of 5 rows and 7 columns:

dim table(4, 6)

 Describe VBScript Procedures

We have two kinds of procedures: The Sub procedure and the Function procedure.

A Sub procedure:

  • is a series of statements, enclosed by the Sub and End Sub statements
  • can perform actions, but does not return a value
  • can take arguments that are passed to it by a calling procedure
  • without arguments, must include an empty set of parentheses ()
Sub mysub()
 some statements
End Sub

or

Sub mysub(argument1,argument2)
 some statements
End Sub

A Function procedure:

  • is a series of statements, enclosed by the Function and End Function statements
  • can perform actions and can return a value
  • can take arguments that are passed to it by a calling procedure
  • without arguments, must include an empty set of parentheses ()
  • returns a value by assigning a value to its name
Function myfunction()
 some statements
 myfunction=some value
End Function

or

Function myfunction(argument1,argument2)
 some statements
 myfunction=some value
End Function

  How to Call a Sub or Function Procedure?

When you call a Function in your code, you do like this:

name = findname()

Here you call a Function called “findname”, the Function returns a value that will be stored in the variable “name”.

Or, you can do like this:

msgbox "Your name is " & findname()

Here you also call a Function called “findname”, the Function returns a value that will be displayed in the message box.

When you call a Sub procedure you can use the Call statement, like this:

Call MyProc(argument)

Or, you can omit the Call statement, like this:

MyProc argument

 Why we use Conditional Statements?

Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.

In VBScript we have three conditional statements:

  • if statement – use this statement if you want to execute a set of code when a condition is true
  • if…then…else statement – use this statement if you want to select one of two sets of lines to execute
  • if…then…elseif statement – use this statement if you want to select one of many sets of lines to execute
  • select case statement – use this statement if you want to select one of many sets of lines to execute

 If….Then…..Else

You should use the If…Then…Else statement if you want to

  • execute some code if a condition is true
  • select one of two blocks of code to execute

If you want to execute only one statement when a condition is true, you can write the code on one line:

if i=10 Then msgbox "Hello"

There is no ..else.. in this syntax. You just tell the code to perform one action if the condition is true (in this case if i=10).

If you want to execute more than one statement when a condition is true, you must put each statement on separate lines and end the statement with the keyword “End If”:

if i=10 Then
   msgbox "Hello"
   i = i+1
end If

There is no ..else.. in this syntax either. You just tell the code to perform multiple actions if the condition is true.

If you want to execute a statement if a condition is true and execute another statement if the condition is not true, you must add the “Else” keyword:

if i=10 then
   msgbox "Hello"
else
   msgbox "Goodbye"
end If

The first block of code will be executed if the condition is true, and the other block will be executed otherwise (if i is not equal to 10).

 

If….Then…..Elseif

You can use the if…then…elseif statement if you want to select one of many blocks of code to execute:

if payment="Cash" then
   msgbox "You are going to pay cash!"
 elseif payment="Visa" then
   msgbox "You are going to pay with visa."
 elseif payment="AmEx" then
   msgbox "You are going to pay with American Express."
 else
   msgbox "Unknown method of payment."
end If

 


Select Case

You can also use the SELECT statement if you want to select one of many blocks of code to execute:

select case payment
 case "Cash"
   msgbox "You are going to pay cash"
 case "Visa"
   msgbox "You are going to pay with visa"
 case "AmEx"
   msgbox "You are going to pay with American Express"
 case Else
   msgbox "Unknown method of payment"
end select

This is how it works: First we have a single expression (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each Case in the structure. If there is a match, the block of code associated with that Case is executed.

 

Describe Looping Statements

Very often when you write code, you want to allow the same block of code to run a number of times. You can use looping statements in your code to do this.

In VBScript we have four looping statements:

  • For…Next statement – runs statements a specified number of times. 
  • For Each…Next statement – runs statements for each item in a collection or each element of an array
  • Do…Loop statement – loops while or until a condition is true
  • While…Wend statement – Do not use it – use the Do…Loop statement instead

For…Next Loop

You can use a For…Next statement to run a block of code, when you know how many repetitions you want.

You can use a counter variable that increases or decreases with each repetition of the loop, like this:

For i=1 to 10
  some code
Next

The For statement specifies the counter variable (i) and its start and end values. The Next statement increases the counter variable (i) by one.

Step Keyword

Using the Step keyword, you can increase or decrease the counter variable by the value you specify.

In the example below, the counter variable (i) is increased by two each time the loop repeats.

For i=2 To 10 Step 2
  some code
Next

To decrease the counter variable, you must use a negative Step value. You must specify an end value that is less than the start value.

In the example below, the counter variable (i) is decreased by two each time the loop repeats.

For i=10 To 2 Step -2
  some code
Next

Exit a For…Next

You can exit a For…Next statement with the Exit For keyword.

 For Each…Next Loop

A For Each…Next loop repeats a block of code for each item in a collection, or for each element of an array.

dim cars(2)
cars(0)="Volvo"
cars(1)="Saab"
cars(2)="BMW"
 
For Each x in cars
  document.write(x & "<br />")
Next

 

 

Do…Loop

You can use Do…Loop statements to run a block of code when you do not know how many repetitions you want. The block of code is repeated while a condition is true or until a condition becomes true.

Repeating Code While a Condition is True

You use the While keyword to check a condition in a Do…Loop statement.

Do While i>10
  some code
Loop

If i equals 9, the code inside the loop above will never be executed.

Do
  some code
Loop While i>10

The code inside this loop will be executed at least one time, even if i is less than 10.

Repeating Code Until a Condition Becomes True

You use the Until keyword to check a condition in a Do…Loop statement.

Do Until i=10
  some code   
Loop

If i equals 10, the code inside the loop will never be executed.

Do
  some code
Loop Until i=10

The code inside this loop will be executed at least one time, even if i is equal to 10.

Exit a Do…Loop

You can exit a Do…Loop statement with the Exit Do keyword.

Do Until i=10
  i=i-1
  If i<10 Then Exit Do
Loop

The code inside this loop will be executed as long as i is different from 10, and as long as i is greater than 10.

 

I believe this post has given you the basic understanding about vbscripting.I will recommend you to go through the following useful sites for understanding more about Vbscripting.

www.w3schools.com/Vbscript/default.asp

http://msdn.microsoft.com/en-us/library/sx7b3k7y(VS.85).aspx

Reference :MSDN

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2 Responses to “Q&A : VB Scripting”


  1. 1 Gowri January 6, 2010 at 6:29 pm

    VB Scripting is a great thing to automate process.Thanks for the brief explanation.

  2. 2 Peter Gwesso May 9, 2011 at 7:14 am

    send me more questions


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