The Internet Encyclopedia (Volume 3)

P1: JDT

WL040C-44 WL040/Bidgoli-Vol III-Ch-51 June 23, 2003 16:33 Char Count= 0

OBJECTS INVBSCRIPT 627

method of the WSH object model’s WScript object. Ref-

erence to WScript.ScriptFullName returns the variant

(subtype string) property of the WScript object that

contains the full path and file name of the script be-

ing executed. WScript.Arguments.Item(0) returns the

first item in the list of command line arguments used

when the script was invoked (an example of a col-

lection). Object event references are typically used in

user-defined subroutine declarations. Thus, on a Web

page containing an HTML <Select> element (i.e., pull-

down menu) named “myChoice,” a programmer could in-

clude a subroutine declared as “Sub myChoiceOnChange

(),” which would then be invoked each time the user

changed his or her selection from that particular

menu.

Intrinsic Object Models

VBScript provides two built-in object models, one intrin-

sic to the language itself, and one included as part of

the Microsoft Scripting Runtime library (and therefore

also available to JScript implementations). The former

includes the regular expression object (RegExp) and the

error object (Err). Note that the RegExp object must be

instantiated using the New key word (as typical for early

binding) rather than the CreateObject method (late bind-

ing) as required for other objects instantiated in VBScript;

thus,

set objMyRegularExpression = New RegExp

The RegExp object allows testing of strings for pattern

matches and manipulation of matches found through the

“Match” object collection (a child of the RegExp object

class).

The Err object is singular, is always available, and

therefore does not need to be explicitly instantiated. The

Err object includes a method to clear an error condition

and properties providing the number and description of

the last error that occurred. It is used in conjunction with

the On Error Resume Next statement for user-defined

error handling.

Version 5.6 of the Microsoft Scripting Runtime Library

provides two important objects, the FileSystemObject, for

accessing file system directory information and reading

from and writing to individual text files, and the Dictio-

nary object, which is similar to associative arrays found

in Perl and other programming languages. The FileSys-

temObject is at the top of an extensive and powerful ob-

ject hierarchy that provides access through a variety of

child objects to the host system’s drives, directories, and

files. “Scripting.FileSystemObject” is the ProgID for the

FileSystemObject. Using methods and properties of the

FileSystemObject you can browse drives and folders of

the host computer, create new folders and text files on the

host computer’s file system, and open existing text files

on the host computer for reading and/or writing (e.g., by

creating and using child TextStream objects). Note, when

using the FileSystemObject (and most other external COM

objects) for client-side scripting in Microsoft Internet Ex-

plorer, Internet Explorer typically warns users that use of

these objects might be unsafe. Users can even configure

Internet Explorer not to allow instantiation and use of

external COM objects. Listing 4 illustrates the use of the

FileSystemObject in WSH.

Finally, the Dictionary object of the Microsoft Scripting

Runtime Library allows you to store and manipulate lists

of key value pairs, i.e., lists of values where each value is

tied to a unique key. “Scripting.Dictionary” is the ProgID

of the Dictionary object. This object has a small set of

properties and methods that allow your script to add and

remove items from the dictionary list, retrieve or alter in-

dividual values by key, change or replace individual keys,

and check to see if a particular key exists in the dictionary

list.

Listing 4:Illustrating the use of FileSystemObject in the con-

text of WSH.

Option Explicit

Const conMyLine =_

"This was written by a VBScript script."

Const conMyFileName = "Temp.txt"

Dim objMyFS, objMyTS

Dim strFileName, strTextLine

set objMyFS = WScript.CreateObject_

("Scripting.FileSystemObject")

strFileName = Replace_

(WScript.ScriptFull Name,_

WScript.ScriptName, conMyFileName)

if objMyFS.FileExists(strFileName) then

set objMyTS = objMyFS.OpenTextFile_

(strFileName)

strTextLine = objMyTS.ReadLine

objMyTS.Close

MsgBox (strTextLine)

else

set objMyTS = objMyFS.CreateTextFile_

(strFileName)

objMyTS.WriteLine(conMyLine)

objMyTS.Close

MsgBox ("Created" & strFileName)

end if

set objMyTS = Nothing

set objMyFS = Nothing

Windows Scripting Host Object Model

The WSH object model consists of a top-level object,

WScript, with properties germane to the script and how

it was invoked, methods for suspending and ending script

execution and creating and using external objects, and

a half-dozen immediate child objects, each providing

access to a service or a function of the host system.

WScript child objects include: WshArguments, a collec-

tion containing any command line arguments used when

invoking the script; WshNetwork, providing access to

network configuration and services; StdIn, StdOut, and

StdErr, specialized read-only or write-only (as appro-

priate) TextStream objects providing access to standard

input and output devices (e.g., keyboard and display);

and WshShell, providing access to a variety of Windows