Visual Basic .NET

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Visual_Basic_.NET

 

Visual Basic .NET

Paradigm	Structured, imperative, object-oriented, declarative, generic, reflective and event-driven
Designed by	Microsoft
Developer	Microsoft
First appeared	2001; 18 years ago
Stable release	2019 (16.2) / July 24, 2019; 4 months ago
Typing discipline	Static, both strong and weak, both safe and unsafe, nominative
Platform	.NET Framework, Mono, .NET Core 3
OS	Chiefly Windows Also on Android, BSD, iOS, Linux, macOS, Solaris and Unix
License	Roslyn compiler: Apache License 2.0
Filename extensions	.vb
Website	docs.microsoft.com/dotnet/visual-basic/
Major implementations
.NET Framework SDK, Roslyn Compiler and Mono
Dialects
Microsoft Visual Basic
Influenced by
Visual Basic
Influenced
Small Basic

Visual Basic .NET (VB.NET) is a multi-paradigm, object-oriented programming language, implemented on the .NET Framework. Microsoft launched VB.NET in 2002 as the successor to its original Visual Basic language. Although the ".NET" portion of the name was dropped in 2005, this article uses "Visual Basic [.NET]" to refer to all Visual Basic languages released since 2002, in order to distinguish between them and the classic Visual Basic. Along with Visual C#, it is one of the two main languages targeting the .NET framework.

Microsoft's integrated development environment (IDE) for developing in Visual Basic .NET language is Visual Studio. Most Visual Studio editions are commercial; the only exceptions are Visual Studio Express and Visual Studio Community, which are freeware. In addition, the .NET Framework SDK includes a freeware command-line compiler called vbc.exe. Mono also includes a command-line VB.NET compiler.

Contents

• 1 Syntax
  • 1.1 Simple example
  • 1.2 Complex example
  • 1.3 Comparison with the classic Visual Basic
    • 1.3.1 Comparative examples
  • 1.4 Comparison with C#
• 2 Examples
  

Syntax

VB.NET uses statements to specify actions. The most common statement is an expression statement, consisting of an expression to be evaluated, on a single line. As part of that evaluation, functions or subroutines may be called and variables may be assigned new values. To modify the normal sequential execution of statements, VB.NET provides several control-flow statements identified by reserved keywords. Structured programming is supported by several constructs including two conditional execution constructs (If … Then … Else … End If and Select Case ... Case ... End Select ) and three iterative execution (loop) constructs (Do … Loop, For … To, and For Each) . The For … To statement has separate initialisation and testing sections, both of which must be present. (See examples below.) The For Each statement steps through each value in a list. 

In addition, in Visual Basic .NET:

• There is no unified way of defining blocks of statements. Instead, certain keywords, such as "If … Then" or "Sub" are interpreted as starters of sub-blocks of code and have matching termination keywords such as "End If" or "End Sub".
• Statements are terminated either with a colon (":") or with the end of line. Multiple-line statements in Visual Basic .NET are enabled with " _" at the end of each such line. The need for the underscore continuation character was largely removed in version 10 and later versions.
• The equals sign ("=") is used in both assigning values to variables and in comparison.
• Round brackets (parentheses) are used with arrays, both to declare them and to get a value at a given index in one of them. Visual Basic .NET uses round brackets to define the parameters of subroutines or functions.
• A single quotation mark (') or the keyword REM, placed at the beginning of a line or after any number of space or tab characters at the beginning of a line, or after other code on a line, indicates that the (remainder of the) line is a comment.
  

Simple example

The following is a very simple VB.NET program, a version of the classic "Hello world" example created as a console application:

Module Module1

    Sub Main()
        ' The classic "Hello, World" demonstration program
        Console.WriteLine("Hello, World!")
    End Sub

End Module

It prints "Hello, world!" on a command-line window. Each line serves a specific purpose, as follows:

Module Module1

This is a module definition. Modules are a division of code, which can contain any kind of object, like constants or variables, functions or methods, or classes, but can't be instantiated as objects like classes and cannot inherit from other modules. Modules serve as containers of code that can be referenced from other parts of a program.

It is common practice for a module and the code file, which contains it, to have the same name; however, this is not required, as a single code file may contain more than one module and/or class definition. 

Sub Main()

It defines a subroutine called "Main". "Main" is the entry point, where the program begins execution.

Console.WriteLine("Hello, world!")

This line performs the actual task of writing the output. Console is a system object, representing a command-line interface (also known as "console") and granting programmatic access to the operating system's standard streams. The program calls the Console method WriteLine, which causes the string passed to it to be displayed on the console.

Instead of Console.WriteLine, one could use MsgBox, which prints the message in a dialog box instead of a command-line window.

Complex example

This piece of code outputs Floyd's Triangle to the console:

Imports System.Console

Module Program

    Sub Main()
        Dim rows As Integer

        ' Input validation.
        Do Until Integer.TryParse(ReadLine_

            ("Enter a value for how many rows to be displayed: "_

            & vbcrlf), rows) AndAlso rows >= 1
            WriteLine("Allowed range is 2 and {0}",_

                      Integer.MaxValue)
        Loop
      
        ' Output of Floyd's Triangle
        Dim current As Integer = 1
        Dim row As Integer 
        Dim column As Integer
        For row = 1 To rows
            For column = 1 To row
                Write("{0,-2} ", current)
                current += 1
            Next

            WriteLine()
        Next
    End Sub

    ' 

    ' Shadows Console.ReadLine with a version which takes a prompt string.
    ' 

Function ReadLine(Optional prompt As String = Nothing) As String If prompt IsNot Nothing Then Write(prompt) End If Return Console.ReadLine() End Function End Module

Comparison with the classic Visual Basic

Whether Visual Basic .NET should be considered as just another version of Visual Basic or a completely different language is a topic of debate. There are new additions to support new features, such as structured exception handling and short-circuited expressions. Also, two important data-type changes occurred with the move to VB.NET: compared to Visual Basic 6, the Integer data type has been doubled in length from 16 bits to 32 bits, and the Long data type has been doubled in length from 32 bits to 64 bits. This is true for all versions of VB.NET. A 16-bit integer in all versions of VB.NET is now known as a Short. Similarly, the Windows Forms editor is very similar in style and function to the Visual Basic form editor. 

The things that have changed significantly are the semantics—from those of an object-based programming language running on a deterministic, reference-counted engine based on COM to a fully object-oriented language backed by the .NET Framework, which consists of a combination of the Common Language Runtime (a virtual machine using generational garbage collection and a just-in-time compilation engine) and a far larger class library. The increased breadth of the latter is also a problem that VB developers have to deal with when coming to the language, although this is somewhat addressed by the My feature in Visual Studio 2005.

The changes have altered many underlying assumptions about the "right" thing to do with respect to performance and maintainability. Some functions and libraries no longer exist; others are available, but not as efficient as the "native" .NET alternatives. Even if they compile, most converted Visual Basic 6 applications will require some level of refactoring to take full advantage of the new language. Documentation is available to cover changes in the syntax, debugging applications, deployment and terminology.

Comparative examples

The following simple examples compare VB and VB.NET syntax. They assume that the developer has created a form, placed a button on it and has associated the subroutines demonstrated in each example with the click event handler of the mentioned button. Each example creates a "Hello, World" message box after the button on the form is clicked. 

Visual Basic 6: 

Private Sub Command1_Click()
    MsgBox "Hello, World"
End Sub

VB.NET (MsgBox or MessageBox class can be used):

Private Sub Button1_Click(sender As object, e As EventArgs)_

                          Handles Button1.Click
    MsgBox("Hello, World")
End Sub

• Both Visual Basic 6 and Visual Basic .NET automatically generate the Sub and End Sub statements when the corresponding button is double-clicked in design view. Visual Basic .NET will also generate the necessary Class and End Class statements. The developer need only add the statement to display the "Hello, World" message box.
• All procedure calls must be made with parentheses in VB.NET, whereas in Visual Basic 6 there were different conventions for functions (parentheses required) and subs (no parentheses allowed, unless called using the keyword Call).
• The names Command1 and Button1 are not obligatory. However, these are default names for a command button in Visual Basic 6 and VB.NET respectively.
• In VB.NET, the Handles keyword is used to make the sub Button1_Click a handler for the Click event of the object Button1. In Visual Basic 6, event handler subs must have a specific name consisting of the object's name ("Command1"), an underscore ("_"), and the event's name ("Click", hence "Command1_Click").
• There is a function called MessageBox.Show in the Microsoft.VisualBasic namespace which can be used (instead of MsgBox) similarly to the corresponding function in Visual Basic 6. There is a controversy about which function to use as a best practice (not only restricted to showing message boxes but also regarding other features of the Microsoft.VisualBasic namespace). Some programmers prefer to do things "the .NET way", since the Framework classes have more features and are less language-specific. Others argue that using language-specific features makes code more readable (for example, using int (C#) or Integer (VB.NET) instead of System.Int32).
• In Visual Basic 2008, the inclusion of ByVal sender as Object, ByVal e as EventArgs has become optional.

The following example demonstrates a difference between Visual Basic 6 and VB.NET. Both examples close the active window.

Visual Basic 6:

Sub cmdClose_Click()
    Unload Me
End Sub

VB.NET:

Sub btnClose_Click(sender As Object, e As EventArgs)_

                   Handles btnClose.Click
    Close()
End Sub

The 'cmd' prefix is replaced by the 'btn' prefix, conforming to the new convention previously mentioned.

Visual Basic 6 did not provide common operator shortcuts. The following are equivalent:

Visual Basic 6:

Sub Timer1_Timer()
    'Reduces Form Height by one pixel per tick
    Me.Height = Me.Height - 1
End Sub

VB.NET:

Sub Timer1_Tick(sender As Object, e As EventArgs)_

    Handles Timer1.Tick
    Me.Height -= 1
End Sub 

Comparison with C#

C# and Visual Basic .NET are Microsoft's first languages made to program on the .NET Framework (later adding F# and more and others have also added languages). Though C# and VB.NET are syntactically different, that is where the differences mostly end. Microsoft developed both of these languages to be part of the same .NET Framework development platform. They are both developed, managed, and supported by the same language development team at Microsoft. They compile to the same intermediate language (IL), which runs against the same .NET Framework runtime libraries. Although there are some differences in the programming constructs, their differences are primarily syntactic and, assuming one avoids the Visual Basic "Compatibility" libraries provided by Microsoft to aid conversion from Visual Basic 6, almost every command in VB has an equivalent command in C# and vice versa. Lastly, both languages reference the same Base Classes of the .NET Framework to extend their functionality. As a result, with few exceptions, a program written in either language can be run through a simple syntax converter to translate to the other. There are many open source and commercially available products for this task.

Examples

Hello World!

Windows Form Application

Requires a button called Button1.

Public Class Form1
    Private Sub Button1_Click(sender As Object, e As EventArgs)_

                              Handles Button1.Click
        MsgBox("Hello world!", MsgBoxStyle.Information, "Hello world!")
    End Sub
End Class 

Hello world! window

Console Application

Module Module1

    Sub Main()
        Console.WriteLine("Hello world!")

       ' Write in the console "Hello world!" and start a new line.
        Console.ReadKey()

       ' The user must press any key before the application ends.
    End Sub
End Module

Speaking

Windows Form Application

Requires a TextBox titled 'TextBox1' and a button called Button1.

Public Class Form1
    
    Private Sub Button1_Click(sender As Object, e As EventArgs)_

                              Handles Button1.Click
        CreateObject("Sapi.Spvoice").Speak(TextBox1.Text)
    End Sub
End Class

Console Application

Module Module1
    Private Voice = CreateObject("Sapi.Spvoice")
    Private Text As String

    Sub Main()
        Console.Write("Enter the text to speak: ")

        ' Say "Enter the text to speak: "
        Text = Console.ReadLine()

        ' The user must enter the text to speak.
        Voice.Speak(Text)

        ' Speak the text the user has entered.
    End Sub
End Module

Version history

Succeeding the classic Visual Basic version 6.0, the first version of Visual Basic .NET debuted in 2002. As of 2017, eight versions of Visual Basic .NET are released. 

2002 (VB 7.0)

The first version, Visual Basic .NET, relies on .NET Framework 1.0. The most important feature is managed code, which contrasts with the classic Visual Basic. 

2003 (VB 7.1)

Visual Basic .NET 2003 was released with .NET Framework 1.1. New features included support for the .NET Compact Framework and a better VB upgrade wizard. Improvements were also made to the performance and reliability of .NET IDE (particularly the background compiler) and runtime. In addition, Visual Basic .NET 2003 was available in the Visual Studio.NET Academic Edition, distributed to a certain number of scholars from each country without cost. 

2005 (VB 8.0)

After Visual Basic .NET 2003, Microsoft dropped ".NET" from the name of the product, calling the next version Visual Basic 2005. 

For this release, Microsoft added many features intended to reinforce Visual Basic .NET's focus as a rapid application development platform and further differentiate it from C#., including:

• Edit and Continue feature
• Design-time expression evaluation
• A pseudo-namespace called "My", which provides:
  • Easy access to certain areas of the .NET Framework that otherwise require significant code to access like using My.Form2.Text = " MainForm rather than System.WindowsApplication1.Forms.Form2.text = " MainForm "
  • Dynamically generated classes (e.g. My.Forms)
• Improved VB-to-VB.NET converter
• A "using" keyword, simplifying the use of objects that require the Dispose pattern to free resources
• Just My Code feature, which hides (steps over) boilerplate code written by the Visual Studio .NET IDE and system library code during debugging
• Data Source binding, easing database client/server development

To bridge the gaps between itself and other .NET languages, this version added:

• Generics
• Partial classes, a method of defining some parts of a class in one file and then adding more definitions later; particularly useful for integrating user code with auto-generated code
• Operator overloading and nullable types
• Support for unsigned integer data types commonly used in other languages

Visual Basic 2005 introduced the IsNot operator that makes 'If X IsNot Y' equivalent to 'If Not X Is Y'. It gained notoriety when it was found to be the subject of a Microsoft patent application.

2008 (VB 9.0)

Visual Basic 9.0 was released along with .NET Framework 3.5 on November 19, 2007.

For this release, Microsoft added many features, including:

• A true conditional operator,
  "If(condition as boolean, truepart, falsepart)"
  to replace the "IIf" function.
• Anonymous types
• Support for LINQ
• Lambda expressions
• XML Literals
• Type Inference
• Extension methods
  

2010 (VB 10.0)

In April 2010, Microsoft released Visual Basic 2010. Microsoft had planned to use Dynamic Language Runtime (DLR) for that release but shifted to a co-evolution strategy between Visual Basic and sister language C# to bring both languages into closer parity with one another. Visual Basic's innate ability to interact dynamically with CLR and COM objects has been enhanced to work with dynamic languages built on the DLR such as IronPython and IronRuby. The Visual Basic compiler was improved to infer line continuation in a set of common contexts, in many cases removing the need for the " _" line continuation characters. Also, existing support of inline Functions was complemented with support for inline Subs as well as multi-line versions of both Sub and Function lambdas.

2012 (VB 11.0)

Visual Basic 2012 was released along .NET Framework 4.5. Major features introduced in this version include:

• Asynchronous programming with "async" and "await" statements
• Iterators
• Call hierarchy
• Caller information
• Global keyword in "namespace" statements
  

2015 (VB 14.0)

Visual Basic 2015 (code named VB "14.0") has been released with Visual Studio 2015. Language features include a new "?." operator to perform inline null checks, and a new string interpolation feature is included to format strings inline.

2017 (VB 15.0)

Visual Basic 2017 (code named VB "15.0") has been released with Visual Studio 2017. Extends support for new Visual Basic 15 language features, and introduces new refactorings that allow organizing source code with one action.

2019 (VB 16.0)

Visual Basic 2019 (code named VB "16.0") has been released with Visual Studio 2019. 

Cross-platform and open-source development

The official VB.NET compiler is written in VB.NET and is available on GitHub as a part of the .NET Compiler platform. The creation of open-source tools for VB.NET development has been slow compared to C#, although the Mono development platform provides an implementation of VB.NET-specific libraries and a VB.NET 8.0 compatible compiler written in VB.NET, as well as standard framework libraries such as Windows Forms GUI library.

SharpDevelop and MonoDevelop are open-source alternative IDEs.

Visual Basic for Applications

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Visual_Basic_for_Applications

 

Visual Basic for Applications

Paradigm	Multi-paradigm
Developer	Microsoft
First appeared	1993; 26 years ago
Stable release	7.1 (Office 2019)
Typing discipline	Static/Dynamic Hybrid, Strong/Weak Hybrid
OS	Microsoft Windows, Mac OS X
License	Commercial proprietary software
Influenced by
QuickBASIC, Visual Basic

Visual Basic for Applications (VBA) is an implementation of Microsoft's event-driven programming language Visual Basic 6, which was declared legacy in 2008, and its associated integrated development environment (IDE). Although pre-.NET Visual Basic is no longer supported or updated by Microsoft, the VBA programming language was upgraded in 2010 with the introduction of Visual Basic for Applications 7 in Microsoft Office applications.

Visual Basic for Applications enables building user-defined functions (UDFs), automating processes and accessing Windows API and other low-level functionality through dynamic-link libraries (DLLs). It supersedes and expands on the abilities of earlier application-specific macro programming languages such as Word's WordBASIC. It can be used to control many aspects of the host application, including manipulating user interface features, such as menus and toolbars, and working with custom user forms or dialog boxes.

As its name suggests, VBA is closely related to Visual Basic and uses the Visual Basic Runtime Library. However, VBA code normally can only run within a host application, rather than as a standalone program. VBA can, however, control one application from another using OLE Automation. For example, VBA can automatically create a Microsoft Word report from Microsoft Excel data that Excel collects automatically from polled sensors. VBA can use, but not create, ActiveX/COM DLLs, and later versions add support for class modules.

VBA is built into most Microsoft Office applications, including Office for Mac OS X (except version 2008), and other Microsoft applications, including Microsoft MapPoint and Microsoft Visio. VBA is also implemented, at least partially, in applications published by companies other than Microsoft, including ArcGIS, AutoCAD, CorelDraw, LibreOffice, Reflection, SolidWorks,, WordPerfect, and UNICOM System_Architect (which supports VBA 7.1).

Design

Code written in VBA is compiled to Microsoft P-Code (pseudo-code), a proprietary intermediate language, which the host applications (Access, Excel, Word, Outlook, and PowerPoint) store as a separate stream in COM Structured Storage files (e.g., .doc or .xls) independent of the document streams. The intermediate code is then executed by a virtual machine (hosted by the host application). Despite its resemblance to many old BASIC dialects (particularly Microsoft BASIC, from which it is indirectly derived), VBA is incompatible with any of them except Visual Basic, where source code of VBA modules and classes can be directly imported, and which shares the same library and virtual machine. Compatibility ends with Visual Basic version 6; VBA is incompatible with Visual Basic .NET (VB.NET). VBA is proprietary to Microsoft and, apart from the COM interface, is not an open standard. 

Automation

Interaction with the host application uses OLE Automation. Typically, the host application provides a type library and application programming interface (API) documentation which document how VBA programs can interact with the application. This documentation can be examined from inside the VBA development environment using its Object Browser.

Visual Basic for Applications programs which are written to use the OLE Automation interface of one application cannot be used to automate a different application, even if that application hosts the Visual Basic runtime, because the OLE Automation interfaces will be different. For example, a VBA program written to automate Microsoft Word cannot be used with a different word processor, even if that word processor hosts VBA.

Conversely, multiple applications can be automated from the one host by creating Application objects within the VBA code. References to the different libraries must be created within the VBA client before any of the methods, objects, etc. become available to use in the application. This is achieved through what is referred to as Early or Late Binding. These application objects create the OLE link to the application when they are first created. Commands to the different applications must be done explicitly through these application objects in order to work correctly.

As an example, VBA code written in Microsoft Access can establish references to the Excel, Word and Outlook libraries; this allows creating an application that --- for instance --- runs a query in Access, exports the results to Excel and analyzes them, and then formats the output as tables in a Word document or sends them as an Outlook email.

VBA programs can be attached to a menu button, a macro, a keyboard shortcut, or an OLE/COM event, such as the opening of a document in the application. The language provides a user interface in the form of UserForms, which can host ActiveX controls for added functionality.

Inter-process communication automation includes the Dynamic Data Exchange (DDE) and RealTimeData (RTD) which allows calling a Component Object Model (COM) automation server for dynamic or realtime financial or scientific data.

Security concerns

As with any common programming language, VBA macros can be created with malicious intent. Using VBA, most of the security features lie in the hands of the user, not the author. The VBA host application options are accessible to the user. The user who runs any document containing VBA macros can preset the software with user preferences. End-users can protect themselves from attack by disabling macros from running in an application or by granting permission for a document to run VBA code only if they are sure that the source of the document can be trusted.

Version history

• VBA was first launched with MS Excel 5.0 in 1993. It became an instant success among developers to create corporate solutions using Excel. Inclusion of VBA with Microsoft Project, Access and Word replacing AccessBASIC and WordBASIC respectively made it more popular.
• VBA 4.0 is the next famous release with a totally upgraded version compared to previous one. Released in 1996, it is written in C++ and became an object oriented language.
• VBA 5.0 was launched in 1997 along with all of MS Office 97 products. The only exception for this was Outlook 97 which used VBScript to automate things.
• VBA 6.0 and VBA 6.1 were launched in 1999, notably with support for COM add-ins in Office 2000. VBA 6.2 was released alongside Office 2000 SR-1.
• VBA 6.3 was released after Office XP, VBA 6.4 followed Office 2003 and VBA 6.5 was released with Office 2007.
• Office 2010 includes VBA 7.0. There are no new features in VBA 7 for developers compared to VBA 6.5 except for 64-bit support. However, after VBA 6.5/Office 2007, Microsoft stopped licensing VBA for other applications.
• Office 2013, Office 2016, and Office 2019 include VBA 7.1.

Development

As of July 1, 2007, Microsoft no longer offers VBA distribution licenses to new customers. Microsoft intended to add .NET-based languages to the current version of VBA ever since the release of the .NET Framework, of which versions 1.0 and 1.1 included a scripting runtime technology named Script for the .NET Framework. Visual Studio .NET 2002 and 2003 SDK contained a separate scripting IDE called Visual Studio for Applications (VSA) that supported VB.NET. One of its significant features was that the interfaces to the technology were available via Active Scripting (VBScript and JScript), allowing even .NET-unaware applications to be scripted via .NET languages. However, VSA was deprecated in version 2.0 of the .NET Framework, leaving no clear upgrade path for applications desiring Active Scripting support (although "scripts" can be created in C#, VBScript, and other .NET languages, which can be compiled and executed at run-time via libraries installed as part of the standard .NET runtime).

Microsoft dropped VBA support for Microsoft Office 2008 for Mac. VBA was restored in Microsoft Office for Mac 2011. Microsoft said that it has no plan to remove VBA from the Windows version of Office.

With Office 2010, Microsoft introduced VBA7, which contains a true pointer data type: LongPtr. This allows referencing 64-bit address space. The 64-bit install of Office 2010 does not support common controls of MSComCtl (TabStrip, Toolbar, StatusBar, ProgressBar, TreeView, ListViews, ImageList, Slider, ImageComboBox) or MSComCt2 (Animation, UpDown, MonthView, DateTimePicker, FlatScrollBar), so legacy 32-bit code ported to 64-bit VBA code that depends on these common controls will not function. This does not affect the 32-bit version Office 2010. VBA7 includes no 64-bit version of the common controls, so it leaves developers with no means to migrate VBA applications to 64-bit. Microsoft suggests contacting the software vendor for 64-bit versions of VBA controls.

Scripting language

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Scripting_language

 

A scripting or script language is a programming language for a special run-time environment that automates the execution of tasks; the tasks could alternatively be executed one-by-one by a human operator. Scripting languages are often interpreted (rather than compiled).

Primitives are usually the elementary tasks or API calls, and the language allows them to be combined into more programs. Environments that can be automated through scripting include software applications, web pages within a web browser, usage of the shells of operating systems (OS), embedded systems, as well as numerous games. A scripting language can be viewed as a domain-specific language for a particular environment; in the case of scripting an application, it is also known as an extension language. Scripting languages are also sometimes referred to as very high-level programming languages, as they operate at a high level of abstraction, or as control languages, particularly for job control languages on mainframes.

The term "scripting language" is also used loosely to refer to dynamic high-level general-purpose languages, such as Perl, PowerShell, Python, and Tcl with the term "script" often used for small programs (up to a few thousand lines of code) in such languages, or in domain-specific languages such as the text-processing languages sed and AWK. Some of these languages were originally developed for use within a particular environment, and later developed into portable domain-specific or general-purpose languages. Conversely, many general-purpose languages have dialects that are used as scripting languages. This article discusses scripting languages in the narrow sense of languages for a specific environment.

The spectrum of scripting languages ranges from very small and highly domain-specific languages to general-purpose programming languages used for scripting. Standard examples of scripting languages for specific environments include: Bash, for the Unix or Unix-like operating systems; ECMAScript (JavaScript), for web browsers; and Visual Basic for Applications, for Microsoft Office applications. Lua is a language designed and widely used as an extension language. Python is a general-purpose language that is also commonly used as an extension language, while ECMAScript is still primarily a scripting language for web browsers, but is also used as a general-purpose language. The Emacs Lisp dialect of Lisp (for the Emacs editor) and the Visual Basic for Applications dialect of Visual Basic are examples of scripting language dialects of general-purpose languages. Some game systems, notably the Second Life virtual world and the Trainz franchise of Railroad simulators have been extensively extended in functionality by scripting extensions (Linden Scripting Language and TrainzScript). In other games like Wesnoth, the variety of actual games played by players are scripts written by other users.

Characteristics

Typical scripting languages are intended to be very fast to learn and write in, either as short source code files or interactively in a read–eval–print loop (REPL, language shell). This generally implies relatively simple syntax and semantics; typically a "script" (code written in the scripting language) is executed from start to finish, as a "script", with no explicit entry point. 

For example, it is uncommon to characterise Java as a scripting language because of its lengthy syntax and rules about which classes exist in which files, and it is not directly possible to execute Java interactively, because source files can only contain definitions that must be invoked externally by a host application or application launcher. 

public class HelloWorld {
  public void printHelloWorld() {
    System.out.println("Hello World");
  }
}

This piece of code intended to print "Hello World" does nothing as main() is not declared in HelloWorld class. 

In contrast, Python allows definition of some functions in a single file, or to avoid functions altogether and use imperative programming style, or even use it interactively. 

print ("Hello World")

This one line of Python code prints "Hello World"; no declarative statement like main() is required here.

A scripting language is usually interpreted from source code or bytecode.^[5] By contrast, the software environment the scripts are written for is typically written in a compiled language and distributed in machine code form.

Scripting languages may be designed for use by end users of a program—end-user development—or may be only for internal use by developers, so they can write portions of the program in the scripting language. Scripting languages typically use abstraction, a form of information hiding, to spare users the details of internal variable types, data storage, and memory management.

Scripts are often created or modified by the person executing them, but they are also often distributed, such as when large portions of games are written in a scripting language.

History

Early mainframe computers (in the 1950s) were non-interactive, instead using batch processing. IBM's Job Control Language (JCL) is the archetype of languages used to control batch processing.

The first interactive shells were developed in the 1960s to enable remote operation of the first time-sharing systems, and these used shell scripts, which controlled running computer programs within a computer program, the shell. Calvin Mooers in his TRAC language is generally credited with inventing command substitution, the ability to embed commands in scripts that when interpreted insert a character string into the script. Multics calls these active functions. Louis Pouzin wrote an early processor for command scripts called RUNCOM for CTSS around 1964. Stuart Madnick at MIT wrote a scripting language for IBM's CP/CMS in 1966. He originally called this processor COMMAND, later named EXEC. Multics included an offshoot of CTSS RUNCOM, also called RUNCOM. EXEC was eventually replaced by EXEC 2 and REXX. 

Languages such as Tcl and Lua were specifically designed as general-purpose scripting languages that could be embedded in any application. Other languages such as Visual Basic for Applications (VBA) provided strong integration with the automation facilities of an underlying system. Embedding of such general-purpose scripting languages instead of developing a new language for each application also had obvious benefits, relieving the application developer of the need to code a language translator from scratch and allowing the user to apply skills learned elsewhere. 

Some software incorporates several different scripting languages. Modern web browsers typically provide a language for writing extensions to the browser itself, and several standard embedded languages for controlling the browser, including JavaScript (a dialect of ECMAScript) or XUL. 

Types

Glue languages

Scripting is often contrasted with system programming, as in Ousterhout's dichotomy or "programming in the large and programming in the small". In this view, scripting is particularly glue code, connecting software components, and a language specialized for this purpose is a glue language. Pipelines and shell scripting are archetypal examples of glue languages, and Perl was initially developed to fill this same role. Web development can be considered a use of glue languages, interfacing between a database and web server. But if a substantial amount of logic is written in script, it is better characterized as simply another software component, not "glue".

Glue languages are especially useful for writing and maintaining:

• custom commands for a command shell;
• smaller programs than those that are better implemented in a compiled language;
• "wrapper" programs for executables, like a batch file that moves or manipulates files and does other things with the operating system before or after running an application like a word processor, spreadsheet, data base, assembler, compiler, etc.;
• scripts that may change;
• Rapid application development of a solution eventually implemented in another, usually compiled, language.

Glue language examples:

• AppleScript
• ColdFusion
• DCL
• Embeddable Common Lisp
• ecl
• Erlang
• JCL
• CoffeeScript
• Julia
• JScript and JavaScript
• Lua
• m4
• Modern Pascal
• Perl (5 and 6)
• PHP
• PowerShell
• Pure
• Python
• Rebol
• Red
• Rexx
• Ruby
• Scheme
• Tcl
• Unix Shell scripts (ksh, csh, bash, sh and others)
• VBScript
• Work Flow Language
• XSLT

Macro languages exposed to operating system or application components can serve as glue languages. These include Visual Basic for Applications, WordBasic, LotusScript, CorelScript, Hummingbird Basic, QuickScript, SaxBasic, and WinWrap Basic. Other tools like AWK can also be considered glue languages, as can any language implemented by a Windows Script Host engine (VBScript, JScript and VBA by default in Windows and third-party engines including implementations of Rexx, Perl, Tcl, Python, XSLT, Ruby, Modern Pascal, Delphi, and C). A majority of applications can access and use operating system components via the object models or its own functions. 

Other devices like programmable calculators may also have glue languages; the operating systems of PDAs such as Windows CE may have available native or third-party macro tools that glue applications together, in addition to implementations of common glue languages—including Windows NT, MS-DOS and some Unix shells, Rexx, Modern Pascal, PHP, and Perl. Depending upon the OS version, WSH and the default script engines (VBScript and JScript) are available.

Programmable calculators can be programmed in glue languages in three ways. For example, the Texas Instruments TI-92, by factory default can be programmed with a command script language. Inclusion of the scripting and glue language Lua in the TI-NSpire series of calculators could be seen as a successor to this. The primary on-board high-level programming languages of most graphing calculators (most often Basic variants, sometimes Lisp derivatives, and more uncommonly, C derivatives) in many cases can glue together calculator functions—such as graphs, lists, matrices, etc. Third-party implementations of more comprehensive Basic version that may be closer to variants listed as glue languages in this article are available—and attempts to implement Perl, Rexx, or various operating system shells on the TI and HP graphing calculators are also mentioned. PC-based C cross-compilers for some of the TI and HP machines used in conjunction with tools that convert between C and Perl, Rexx, AWK, as well as shell scripts to Perl, Modern Pascal, VBScript to and from Perl make it possible to write a program in a glue language for eventual implementation (as a compiled program) on the calculator. 

Job control languages and shells

A major class of scripting languages has grown out of the automation of job control, which relates to starting and controlling the behavior of system programs. (In this sense, one might think of shells as being descendants of IBM's JCL, or Job Control Language, which was used for exactly this purpose.) Many of these languages' interpreters double as command-line interpreters such as the Unix shell or the MS-DOS COMMAND.COM. Others, such as AppleScript offer the use of English-like commands to build scripts. 

GUI scripting

With the advent of graphical user interfaces, a specialized kind of scripting language emerged for controlling a computer. These languages interact with the same graphic windows, menus, buttons, and so on that, a human user would. They do this by simulating the actions of a user. These languages are typically used to automate user actions. Such languages are also called "macros" when control is through simulated key presses or mouse clicks, uas well as tapping or pressing on a touch-activated screen. 

These languages could in principle be used to control any GUI application; but, in practice their use is limited because their use needs support from the application and from the operating system. There are a few exceptions to this limitation. Some GUI scripting languages are based on recognizing graphical objects from their display screen pixels. These GUI scripting languages do not depend on support from the operating system or application. 

Application-specific languages

Application specific languages can be split in many different categories, i.e. standalone based app languages (executable) or internal application specific languages (postscript, xml, gscript as some of the widely distributed scripts, respectively implemented by Adobe, MS and Google) among others include an idiomatic scripting language tailored to the needs of the application user. Likewise, many computer game systems use a custom scripting language to express the programmed actions of non-player characters and the game environment. Languages of this sort are designed for a single application; and, while they may superficially resemble a specific general-purpose language (e.g. QuakeC, modeled after C), they have custom features that distinguish them. Emacs Lisp, while a fully formed and capable dialect of Lisp, contains many special features that make it most useful for extending the editing functions of Emacs. An application-specific scripting language can be viewed as a domain-specific programming language specialized to a single application. 

Extension/embeddable languages

A number of languages have been designed for the purpose of replacing application-specific scripting languages by being embeddable in application programs. The application programmer (working in C or another systems language) includes "hooks" where the scripting language can control the application. These languages may be technically equivalent to an application-specific extension language but when an application embeds a "common" language, the user gets the advantage of being able to transfer skills from application to application. A more generic alternative is simply to provide a library (often a C library) that a general-purpose language can use to control the application, without modifying the language for the specific domain. 

JavaScript began as and primarily still is a language for scripting inside web browsers; however, the standardisation of the language as ECMAScript has made it popular as a general-purpose embeddable language. In particular, the Mozilla implementation SpiderMonkey is embedded in several environments such as the Yahoo! Widget Engine. Other applications embedding ECMAScript implementations include the Adobe products Adobe Flash (ActionScript) and Adobe Acrobat (for scripting PDF files). 

Tcl was created as an extension language but has come to be used more frequently as a general-purpose language in roles similar to Python, Perl, and Ruby. On the other hand, Rexx was originally created as a job control language, but is widely used as an extension language as well as a general-purpose language. Perl is a general-purpose language, but had the Oraperl (1990) dialect, consisting of a Perl 4 binary with Oracle Call Interface compiled in. This has however since been replaced by a library (Perl Module), DBD::Oracle.

Other complex and task-oriented applications may incorporate and expose an embedded programming language to allow their users more control and give them more functionality than can be available through a user interface, no matter how sophisticated. For example, Autodesk Maya 3D authoring tools embed the MEL scripting language, or Blender which uses Python to fill this role.

Some other types of applications that need faster feature addition or tweak-and-run cycles (e.g. game engines) also use an embedded language. During the development, this allows them to prototype features faster and tweak more freely, without the need for the user to have intimate knowledge of the inner workings of the application or to rebuild it after each tweak (which can take a significant amount of time). The scripting languages used for this purpose range from the more common and more famous Lua and Python to lesser-known ones such as AngelScript and Squirrel. 

Ch is another C compatible scripting option for the industry to embed into C/C++ application programs.