Do While...Loop

The Do While...Loop command enables you to run a script. as long as a certain condition is in effect

Example：MonitorForChangedDiskSpace.vbs

'Header information section,define the variabl and on error resume Next
Option Explicit
On Error Resume Next
Dim colMonitoredDisks
Dim objWMIService
Dim objDiskChange
Dim strComputer
Dim startTime 'snapTime used for timer Function

'reference information secton
Const LOCAL_HARD_DISK = 3 'the driveType value from SDK
Const RUN_TIME = 1000 'time to allow the script. to run in seconds
strComputer = "."
startTime = Timer

'Worker and Output Information section
Set bjWMIService = GetObject("winmgmts:\\" & strComputer & "\root\cimv2")
Set colMonitoredDisks = objWMIService.ExecNotificationQuery _
   ("Select * from __instancemodificationevent within 10 where " _
     & "TargetInstance ISA 'Win32_LogicalDisk'")
Do While True
snapTime = Timer
 Set bjDiskChange = colMonitoredDisks.NextEvent
  If objDiskChange.TargetInstance.DriveType = LOCAL_HARD_DISK Then
  WScript.echo "diskSpace on " &_
  objDiskChange.TargetInstance.deviceID &_
  " has changed. It now has " &_

  objDiskChange.TargetInstance.freespace &_
  " Bytes free."
  End If
  If (snapTime - startTime) > RUN_TIME Then
  Exit Do
  End If
Loop
WScript.Echo FormatNumber(snapTime-startTime) & " seconds elapsed. Exiting now"
WScript.quit

For...Next VS For Each...Next

An important difference between For Each...Next and For...Next is that with For Each...Next, you don't have to know how many times you want to do something. With the For...Next construct, you must know exactly how many times you want to do something.

例子DisplayProcessInformation.vbs

'Header information section,define the variabl and on error resume Next
Option Explicit
On Error Resume Next
Dim objWMIService
Dim objItem
Dim i

'reference information sectuin,define two constants
Const MAX_LOOPS = 8, ONE_HOUR = 3600000

'Worker and Output Information, connects to WMI and then executes a query
'that lists all Win32 processes running on the machine
'query chooses everything from the Win32 process, but only if the process ID is not equal to 0
'(the system idle process)
For i = 1 To MAX_LOOPS
Set bjWMIService = GetObject("winmgmts:").ExecQuery _
  ("SELECT * FROM Win32_Process where processID <> 0")
WScript.Echo "There are " & objWMIService.count &_
 " processes running " & Now
 For Each objItem In objWMIService
    WScript.Echo "Process: " & objItem.Name
    WScript.Echo Space(9) & objItem.commandline
    WScript.Echo "Process ID: " & objItem.ProcessID
    WScript.Echo "Thread Count: " & objItem.ThreadCount
    WScript.Echo "Page File Size: " & objItem.PageFileUsage
    WScript.Echo "Page Faults: " & objItem.PageFaults
    WScript.Echo "Working Set Size: " & objItem.WorkingSetSize
    WScript.Echo vbNewLine  ' add a blank line
  Next
  WScript.Echo "******PASS COMPLETE**********"
  WScript.Sleep ONE_HOUR    'wscript. sleep method, the time expression with milliseconds
Next

Compareing to Variable,there are several advantages by using a constant

1 The script. is easier to read

2 The script. is easier to revise

3 The script. is easier to reuse

Wrong example for variable

Option Explicit
On Error Resume Next

Dim total
Dim FirstValue
Dim SecondValue

FirstValue = 1
SecondValue = 3
Total = FirstValue + SecondValue

WScript.Echo " the total of " & FirstValue & " and " & _
  SecondValue & " Is " & (total)
FirstValue = Total
WScript.Echo " the total of " & FirstValue & " and " & _
  SecondValue & " Is " & (Total)

Executing the scripting The result is wrong like below:

C:\script.vbs H:CScript

Microsogt <R> Windows Script. Host Version 5.7

Copyright <C> Microsoft Corporation. All right reserved.

the total of 1 and 3 Is 4

the total of 4 and 3 Is 4

例子CollectionOfDrives.vbs

Option Explicit
On Error Resume Next
Dim colDrives 'the collection that comes from WMI
Dim drive   'an individual drive in the collection
Const DriveType = 3 'Local drives. From the SDK

set colDrives =_
GetObject("winmgmts:").ExecQuery("select size,freespace " &_
"from Win32_LogicalDisk where DriveType =" & DriveType)

For Each drive in colDrives 'walks through the collection
WScript.Echo "Drive: " & drive.DeviceID
WScript.Echo "Size: " & drive.size
WScript.Echo "Freespace: " & drive.freespace
Next

For Each...Next，描述的是个体和集合的概念，只要存在集合的概念，应第一考虑For Each...Next的用法，例如

files, and folders are returned as a collection from the fileSystemObject

From
Microsoft® VBScript. Step by Step
By Ed Wilson

例1 DisplayAdminTools.vbs

Set bjshell = CreateObject("Shell.Application")
Set bjNS = objshell.namespace(&h2f)
Set colitems = objNS.items
For Each objitem In colitems
WScript.Echo objitem.name
Next

例2 DisplayComputerNamesWithComments.vbs

'This script. displays various Computer Names by reading the registry

Option Explicit     'forces the scripter to declare variables
On Error Resume Next 'tells VBScript. to go to the next line
                 'instead of exiting when an error occurs
'Dim is used to declare variable names that are used in the script
Dim objShell
Dim regActiveComputerName, regComputerName, regHostname
Dim ActiveComputerName, ComputerName, Hostname
'When you use a variable name and then an equal sign (=)
'you're saying the variable contains the information on the right.
'The registry keys are quite long, so make them easier to read on
'a single screen by splitting the line in two.

regActiveComputerName = "HKLM\SYSTEM\CurrentControlSet" & _
    "\Control\ComputerName\ActiveComputerName\ComputerName"
regComputerName = "HKLM\SYSTEM\CurrentControlSet\Control" & _
    "\ComputerName\ComputerName\ComputerName"
regHostname = "HKLM\SYSTEM\CurrentControlSet\Services" & _
    "\Tcpip\Parameters\Hostname"

Option Explicit
On Error Resume Next
Dim objShell
Dim regLogonUserName, regServiceInformation, regGPServer
Dim regLogonServer, regDNSdomain
Dim LogonUserName, ServiceInformation, GPServer
Dim LogonServer, DNSdomain
regLogonUserName = "HKEY_CURRENT_USER\Software\Microsoft\" & _
    "Windows\CurrentVersion\Explorer\Logon User Name"
regServiceInformation = "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ServiceCurrent"
regGPServer = "HKEY_CURRENT_USER\Software\Microsoft\Windows\" & _
    "CurrentVersion\Group Policy\History\DCName"
regLogonServer = "HKEY_CURRENT_USER\Volatile Environment\" & _
    "LOGONSERVER"
regDNSdomain = "HKEY_CURRENT_USER\Volatile Environment\" & _
    "USERDNSDOMAIN"
Set bjShell = CreateObject("WScript.Shell")
LogonUserName = objShell.RegRead(regLogonUserName)
ServiceInformation = objShell.RegRead(regServiceInformation)
GPServer = objShell.RegRead(regGPServer)
LogonServer = objShell.RegRead(regLogonServer)
DNSdomain = objShell.RegRead(regDNSdomain)
WScript.Echo LogonUserName & " is currently Logged on"
WScript.Echo ServiceInformation & " is the current service current"
WScript.Echo GPServer & " is the current Group Policy Server"
WScript.Echo LogonServer & " is the current logon server"
WScript.Echo DNSdomain & " is the current DNS domain"

From
Microsoft® VBScript. Step by Step
By Ed Wilson

例1

定义一个数组, 包含5个元素,　都是随机整数(随便输入), 要求把他们按照从大到小的顺序排列起来

Option Explicit
Dim a(4)
Dim i
Dim j
Dim temp

For  i =0  to 4
a(i) = inputbox ("请输入第" &(i+1) &"个元素 ")
Next

For i = 0  to 4
 For j = (i+1) to 4
  If  a(i) < a(j) Then
   temp = a(i)
   a(i) = a(j)
   a(j) = temp
  End If
 Next
Next
msgbox (a(0)&" "&a(1)&" "&a(2)&" "&a(3)&" "&a(4))

VBScript是Visual Basic Script的简称，有时也被缩写为VBS。VBScript是微软开发的一种脚本语言，可以看作是VB语言的简化版，与VBA的关系也非常密切。它具有原语言容易学习的特性。目前这种语言广泛应用于网页和ASP程序制作，同时还可以直接作为一个可执行程序。用于调试简单的VB语句非常方便。

由于VBScript可以通过Windows脚本宿主调用COM，因而可以使用Windows操作系统中可以被使用的程序库，比如它可以使用Microsoft Office的库，尤其是使用Microsoft Access和Microsoft SQL Server的程序库，当然它也可以使用其它程序和操作系统本身的库。在实践中VBScript一般被用在以下三个方面：

Windows操作系统

VBScript可以被用来自动地完成重复性的Windows操作系统任务。在Windows操作系统中，VBScript可以在Windows Script. Host的范围内运行。Windows操作系统可以自动辨认和执行*.VBS和*.WSF两种文档格式，此外Internet Explorer可以执行HTA和CHM文档格式。VBS和WSF文档完全是文字式的，它们只能通过少数几种对话窗口与用户通讯。HTA和CHM文档使用HTML格式，它们的程序码可以象HTML一样被编辑和检查。在WSF、HTA和CHM文档中VBScript和JavaScript的程序码可以任意混合。HTA文档实际上是加有VBS、JavaScript成分的HTML文档。CHM文档是一种在线帮助，用户可以使用专门的编辑程序将HTML程序编辑为CHM。

网页浏览器（客户端的VBS）

网页中的VBS可以用来控制客户端的网页浏览器（以浏览器执行VBS程序）。VBS与JavaScript在这一方面是竞争者，它们可以用来实现动态HTML，甚至可以将整个程序结合到网页中来。

至今为止VBS在客户方面未能占优势，因为它只获得Microsoft Internet Explorer的支持（Mozilla Suite可以透过安装一个包来支持VBS）。而JavaScript则受到所有网页浏览器的支持。在Internet Explorer中VBS和JavaScript使用同样的权限，它们只能有限地使用Windows操作系统中的对象。

网页服务器（服务器方面的VBS）

在网页服务器方面VBS是微软的Active Server Pages的一部分，它与JavaServer Pages和PHP是竞争对手。在这里VBS的程序码直接嵌入到HTML页内，这样的网页以ASP结尾。网页服务器Internet信息服务执行ASP页内的程序部分并将其结果转化为HTML传递给网页浏览器供用户使用。这样服务器可以进行数据库闻讯并将其结果放到HTML网页中。

语言

VBScript主要的优点有：

• 由于VBScript由操作系统，而不是由网页浏览器解释，它的文档比较小。
• 易学。
• 在所有2000 / 98SE以后的Windows版本都可直接使用。
• 可以使用其它程序和可使用的对象（尤其Microsoft Office）。

缺点有：

• 现在VBS无法作为电子邮件的附件了。Microsoft Outlook拒绝接受VBS为附件，收信人无法直接使用VBS附件。
• VBS的各种编辑器不受欢迎。
• 操作系统没有任何特别的保护设施。VBS程序与其它JS、EXE、BAT或CMD程序一样对待。操作系统没有监察恶意功能的能力。

和VB的对比

不能为变量定义类型

在VB中，为变量定义类型使用Dim变量名As类型

但是在VBScript中这样写是错误的。只能使用Dim变量名，解释器会自动根据赋值的类型定义变量类型。

不能使用条件编译

在VB中，可以使用#If…Then、#ElseIf…Then、#Else、#End If、#Const… = …等语句定义编译时使用的语句

而由于VBScript不需要编译即可直接执行，所以并不需要条件编译语句。

安全性

微软决定Outlook和Outlook Express中的HTML邮件可以使用VBScript后出现了许多利用Windows Script. Host和ActiveX的功能的电脑病毒。这些病毒之所以能够传播开来也是因为一开始这些系统功能完全未受保护。虽然VBScript和JavaScript使用同样的使用操作系统的功能的安全措施，今天呼唤这些功能被看作不符合标准。

一般很难保护VBScript的程序码不被用户看到。

[使用组件的优点]

[禁用com组件可能导致的问题]

[手动启动COM组件操作方法]