VBScript Tutorials | Automation Dojos

VBS Part 2 – Fundamentals and Concepts

Tushar Sharma — Thu, 20 Dec 2012 12:09:34 +0000

VBS Part 2 – Fundamentals and Concepts | As Published On Automation Dojos

Having gone through the Introductory part, it is time to look at some crucial fundamentals and concepts. This article is to refresh some of the key facts and features of VBScript. In the least, you should consider the following six points for developing a fundamental understanding of VBScript.

Though we will cover these concepts in depth along with examples in the subsequent tutorials, but for now these brief points are enough for you to understand ‘what you can or should do with VBScript’. So without further ado, let’s jump on to these concepts.

VBScript is a Scripting Language

‘VBScript’ is a ‘scripting language’! What does this mean? Well, a vague difference between a programming and scripting is that a scripting language is not pre-compiled until runtime and hence while the end product of a programming language is mostly a compiled binary executable program (example; .exe), the end product of a scripting language is rather the source code itself (example; .vbs file)!
Hence unlike C++, VB or other compiled programming languages, the ‘VBScript’ is essentially an ‘interpreted language’ which is interpreted by ‘VBScript Engine’ at runtime i.e. every time the code is actually executed it is interpreted (or compiled internally).

For detailed explanation around interpreted and compiled languages, please refer to the earlier article ‘Interpreted Vs Compiled languages‘

VBScript Supports ‘Late Binding’

Since VBScript is a not a compiled language, hence natively it supports only ‘Late Binding’. Therefore unlike the ‘Early Binding’ scenario, in case of VBScript being the ‘Late Binding’ language, the binding does not occur until the program is actually executed.

In this scenario the program usually performs frequent registry or namespace lookups upon execution to access the information about the ‘COM Object’, consequently, any issues with the COM information are not discovered until actual execution. For further reading around this concept, please refer to dedicated article on ‘Early Bound Vs Late Bound‘

Loosely Typed Language

When it comes to ‘Data Types’, VBScript is a ‘loosely typed language’. What this means is that the programmer does not have to declare the ‘Data Type’ of variables in advance. Stating it the other way, VBScript does not provide any means for declaring the ‘Data Types’ for the variables and rather uses a generic or universal data type called the ‘Variant’ which can logically hold any type of value by means of its ‘Sub-Type’

Such a strategy of ‘having and not having data type’ simultaneously is manifested by the concept of ‘Variant’ and its ‘Sub-Type’. Summing-up this by means of a vague analogy, “all variables in VBScript have a default ‘data type called variant’ which is equivalent of ‘no data type’, however, each variant has an associated ‘Sub-Type’ which could be a string, integer, float” etc. Together they manifest the ‘having and not-having’ strategy. More details around this have been discussed in the below section

Single and Universal Data Type

As discussed above, VBScript has only one Data Type which is called the ‘Variant’. This ‘Variant’ is a special type of data type in the sense that it can logically hold almost any type of value e.g. String, Integer, Date, time etc. But this does not mean the VBScript is totally unaware about ‘Data Types’, in order to facilitate VBScript with the intelligence to recognize and deal with ‘Data Types’ it has a special feature known as the ‘SubType’. This ‘SubType’ is kind of ‘Data Type’ of the ‘Variant’ itself. For better understanding Imagine this :

When you declare a variable it automatically gets the ‘Variant’ data type assigned to it. But when you actually put some value in this variable then VBScript assigns the appropriate Sub Type (data type) for this value. You do have means to force the data types or query the data types from there onwards.

So in VBScript, you can solve the dilemma of Data Types by asking the ‘Variant’ that, what is it’s SubType. Now, this might complicate things further hence we will leave it here on the worth mentioning note that – the ‘Variant’ is the only data type supported by VBScript and hence it is the only data type returned by VBScript functions.

Object Model and Libraries

VBScript does not have any proprietary object model of its own! That is to say that if you want to access say for example ‘FileSystem’ or ‘Network’ objects and namespace, VBScript alone cannot help you. It has no way to directly talk to these resources.

But the best part is, that it can hook to most of the COM Components or Servers and exploit them to get the work done. Hence whether you need to play with databases (ADO) or XMLs (DOM) or HTML (DOM) or any other supported COM stuff, it’s a piece of cake for VBS!

Apart from being such a COM Master, it has got some very cool good friends from the same Microsoft family; namely the ‘WSH’, ‘WMI’ and ‘Scripting Runtime Library’. You can literally get almost any scripting or automation task done on windows if you are able to make VBScript work together with these friends.

COM Enabled and COM Automation

On the last note, VBScript is a fully ‘COM-Enabled’ scripting language and hence can very well work with a variety of COM Components / Servers. The worth mentioning point is that VBScript works only with the COM Objects which implement an ‘IDispatch’ interface.

Moreover, VBScript supports COM scripting which is to say that you can create your own ‘Custom Classes’ and their methods and properties in VBScript. This gives you increased power while using VBScript. By coding ‘classes’ you can make your code more robust, modular and reusable.

The post VBS Part 2 – Fundamentals and Concepts appeared first on Automation Dojos.

VBS Part 1 – Introduction and Background

Tushar Sharma — Sat, 10 Nov 2012 11:09:33 +0000

VBS Part 1 – Introduction and Background | As Published On Automation Dojos

At the upfront, this theoretical article might look boring to most of us but still, it is advisable to know about our scripting friend before we start interacting and dealing with it. This is to provide a brief background of VBS, its purpose, origin etc., and if we don’t let go our patience it does turn out to be interesting! In this article, we would briefly discuss about – ‘Windows Script’, ‘Microsoft Visual Basic Family’, ‘VBScript’ background, history and versions.

To start with, the commonly referred to as ‘VB Script’ was developed by Microsoft and hence officially known as the ‘Microsoft’s Visual Basic Scripting Edition‘. It is one of the important members of the ‘Windows Script Technology’ which consists of a total of two members.

Windows Script Technology

The ‘Windows Script‘ is the technology which is the backbone of scripting on Windows platform. It has been manifested as two ‘Script Engines’. Although it is not recommended because of the resulting complexity but these two scripting languages can be included in parallel within a single project and should work perfectly fine!

Windows Script Engines

Visual Basic Scripting Edition (VBScript)
Microsoft JScript

Under this ‘Windows Script‘ banner, Microsoft provides an array of supporting features and technologies which includes tools like – debuggers, script encoders besides the COM libraries and object models like – Runtime Library (scrrun.dll), WSH, WMI, ADSI, DOM and many more.

We will discuss more about ‘VBScript’ in this article as well as in subsequent posts, but for ‘JScript’ we will put an end by saying that it is Microsoft’s implementation of ‘ECMA Scripting Standards and Specification‘. For reference the Netscape’s ‘JavaScript’ as well is an implementation of the same ECMA specification and hence there is a common misconception that both JScript and JavaScript are same but officially it might be wrong to say that.

The Microsoft VB Family

The ‘VBScript’ belongs to the Microsoft VB family, more precisely it is a subset of the ‘Microsoft’s Visual Basic Language‘, this is quite obvious when we look at the similarties in the syntax of the both. The VB family comprises of three members –

VB Family Members

Visual Basic Language
Visual Basic for Applications (VBA) and
Visual Basic Scripting Edition (VBScript)

Unlike the rest of the two members, the VBScript is typically a ‘scripting language‘ hence it inherits all the features and constraints of a ‘scripting language’. Since the VB and VBA are not in-scope of this article hence rather than ‘muddying the water’, we would restrict ourselves to VBScript. As with any scripting language VBScript is –

Windows Script Engines

‘Interpreted at Runtime’
Requires a ‘Host‘ to run on windows and
Does not support ‘Early Binding‘

Besides the above, it is a ‘Loosely Typed Language‘ which means it uses a ‘universal data‘ type (variant) and does not constraints the programmer to specify data types for variables while scripting. You can find more details and explanation on the above in related sections.

History and Background

Historically, VBScript was probably first released (version 1.0) and shipped with Internet Explorer (MSIE 3.0) in 1996. It was intended to be used by web-developers to enhance their ‘client-side scripting’ capabilities.

Nearly a year after, VBScript (version 2.0) was released with some added ‘server-side scripting’ capabilities for Internet Information Server (IIS) which was quite well leveraged with ASP. It was since then, that VBScript quickly claimed its right place. With this success, VBScript (version 3.0) was quickly introduced in Outlook 98 and for the first time appeared with ‘Windows Script Host‘ (WSH 1.0).

Together with ‘Windows Script Host‘ (WSH) which supported any ‘ActiveX Scripting‘ languages, VBScript proved a boon to system administrators by providing the capability to manage and control system resources via VBScripts and other ‘ActiveX scripting‘ languages.

Besides all this, VBScript still lacked any native ‘Object Model‘ and hence soon after, it was supplemented with a ‘Runtime Library‘ providing some ‘Object Model‘. This ‘Script Runtime Library‘ was implemented as ‘scrrun.dll‘ which primarily introduced ‘Dictionary‘ and ‘Filesystem (FSO) object models’.

During the early launch days of VBScript, it had to face a tough competition with another scripting language that preceded it – ‘JavaScript’. Moreover unlike VBScript the ‘Netscape’s‘ support for ‘JavaScript‘ did boost the acceptance of ‘JavaScript‘ in the market rather then VBScript. But due to Microsoft’s committment towards VBScript and subsequent inclusion of VBScript in number of Microsoft products like – IIS, Internet Explorer, Outlook and WSH made VBScript to survive the competition till date.

Latest and Significant Versions

Over the years because of Microsoft’s commitment to VBScript, there have been considerable releases of VBScript each of them adding more or less to it’s feature set. You can find detailed information about VBscript versions on this page on MSDN.

The latest version of VBScript available at the time of this article (Sept 2009) is VBScript version 5.8 available with Internet Explorer v8. However if you ask me the most significant release still remains the VBScript version 5.0. Since it was this VBScript version 5.0 in which Microsoft introduced the – ‘Class Objects’, ‘Class Statement’, ‘Property Let, Get and Set’, ‘Regular Expressions’, ‘Events’, Timer‘, etc.

Applied VBScript (The Playground)

As described above VBScript was meant to be ‘client-side scripting‘ language which holds true to the good extent till date besides its capabilities and usage in ‘server-side scripting‘ in conjunction with HTML, ASP or others. The ‘.HTC’ files being the most basic example of webpage and VBScript collaboration.

Apart from this web arena, VBScript is predominantly popular in ‘system administration‘ domain and of course proves as a good aid in related ‘system side development’ wherein it fits very well along with WSH, WMI, ADSI, ADO etc.

Moreover, to add to its importance and usage – The latest playground is of course HP’s ‘Quick Test Pro‘ which has considerably raised the popularity of VBScript among the ‘Software Testing Community’.

The post VBS Part 1 – Introduction and Background appeared first on Automation Dojos.