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Windows Script Components Have a COM-ing Effect

By The Microsoft Scripting Guys

Doctor Scripto at work

There's a timeworn joke about a boy who visits his grandfather in a retirement home for comedians. Grandpa takes him into a lounge where a bunch of old guys are sitting around quietly smoking stogies. Suddenly, somebody calls out "47," and everybody cracks up. Then another one says "102" and they all groan.

The boy is puzzled, so he asks his grandad what's going on. "Well, sonny boy," the old man says, "for years we've spent all our time sitting around telling jokes. And by now we've all heard each others' jokes so many times, we don't need to tell the whole joke any more: we just have a number for each joke."

So the boy screws up his courage and pipes up: "5." Stony silence. And his grandfather whispers to him, "Nice try, sonny boy, but it's all in the delivery."

This ancient excuse for humor probably came from the Borscht Belt via a Woody Allen movie or some place like that – unlike the old comics, the memory for details of at least one of the Scripting Guys is not as sharp as it used to be. Actually, though, the joke reminded us of some code we've been playing around with. What was that now? Wait a minute, it's on the tip of my tongue. Oh, yeah …

Windows Script Components.

On This Page

Typing or Type Library?
WSC Me Away
Whatever You Do, Keep COM
What's In It For Me?
Creating Script Components
Calling a Script Component in a Script
Post-Script


Typing or Type Library?

Do you like to type? The Scripting Guys do. There's no feeling quite like firing off a long command line at breakneck speed, hitting that Enter button, and watching something impressive happen.

Doctor Scripto

Still, when you're writing scripts typing gets old fast. Of course, most of us cut and paste a lot, but when we do, it's easy to inadvertently miss a line or to include extra lines or characters, botch line endings, and otherwise introduce infuriating errors into our scripts.

Have you ever had some chunks of code that you find yourself typing or pasting over and over again? At some point you might put them into a separate file so you can copy them more easily, or maybe into a code snippet if your scripting environment offers them.

Wouldn't it be handy to be able to give that piece of code a label so you could call it without actually adding all the lines to your script? Many system-level programming languages have a way to do this – things like the #include preprocessor directive in C. But in scripting it's been one of those nice-to-haves that no one seemed to get around to implementing.

Funny thing is, while it's not quite as concise as "47," a scripting "include" has been part of Windows Script all along.

WSC Me Away

A Windows Script Component is just an XML file with a particular schema and a file extension of ".wsc". It can contain properties, functions and subroutines written in script.

Functionally, you can think of it as a text file impersonating a Component Object Model (COM) component. You heard us right: you write a simple text file using XML that wraps script code: VBScript, JScript, or any other WSH-compatible language. Then you can register the file, or component, and call its contents – from scripting languages to system-level programming languages – like any other COM component. You can also call it without registering it, which we'll get to a bit later.

What's going on here?

If you've done much Windows system administration scripting, you've probably encountered enough different COM scripting libraries to get a practical idea of how to work with them. When you use a line of code like this:



Set objWMIService = GetObject("winmgmts:")



you're invoking the hidden powers of the Windows Management Instrumentation (WMI) COM scripting library, which resides within chunks of C++ code deep within the entrails of the Windows operating system.

WMI is a service that's already running, so you use the VBScript GetObject method to bind to the WMI service COM object with the winmgmts: moniker. Once you have connected to WMI, you can use it to call any of its methods or properties and work with any of the thousand or more WMI classes.

Similarly, when you use:



Set objExcel = CreateObject("Excel.Application")



you're creating an instance of and getting a reference to the Excel COM component, using it's programmatic identifier (progID), Excel.Application. With this simple act, you are placing the considerable capabilities of the Excel scripting object model at the disposal of your script. Here, too, the code you're calling into is headquartered somewhere within the vast Office binaries.

Experienced scripters will probably have seen these two lines many times, so they should have some idea of what COM can do for them.

Whatever You Do, Keep COM

While the top level of COM functionality may be familiar, beneath the hood COM still works in mysterious ways for most of us. But it's really not that confusing.

According to Doctor Scripto, COM is a sort of trade agreement for applications. Only instead of committing to certain levels of tariffs or subsidies, when programs use COM they agree to implement certain interfaces and operate in certain ways. These standards let code modules that have signed the COM treaty communicate with other signatory code modules with some confidence in what they will find there and what they can do with it.

System-level languages such as C++ enable you to write your own COM components as parts of executables or DLLs and make them available to other applications and scripts. Windows Script Components let scripts get into the COM market as producers as well as consumers.

Then again, maybe this really is confusing. Doctor Scripto has a talent for zen koans that leave you scratching your head, so we're not going to let him belabor the point any further here. COM has been explained elsewhere in exquisite detail, so we're going to refer you there.

If COM is new to you, a good place to start is the discussion of COM objects in the "VBScript Primer" chapter of the Windows 2000 Scripting Guide. For a technical discussion targeted at developers, see "The Component Object Model: A Technical Overview" on MSDN.

We encourage you to pursue the backstory of COM at your leisure (What? You don't have any leisure?) But for now, let's return to a question that you must be asking by now.

What's In It For Me?

So why would a scripter want to create and use Windows Script Components?

When we find that we're repeating the same code in a lot of scripts, Windows Script Components can offer a convenient and powerful solution. And for an organization, script components provide a way to standardize useful script modules and share them in a way that allows all the scripts used in that organization to call them.

For example, you could use script components to encapsulate frequently used code, such as code for reading and writing text files or sorting arrays and collections. WSC files are also useful for wrapping enumerations and effectively imitating a type library, which you can't access with scripting languages.

If you have any scripts or chunks of script code that you'd like to share with other scripts and applications, Windows Script Components may be worth a try.

As always, a code example is worth ten thousand words (inflation), so let's look at how to create script components and use them in scripts.

Note

There is an alternative way to do something similar to what script components do. You can read a script file into a string with the Script Runtime FileSystemObject and then use the VBScript Execute statement to call into that script code. It takes a few more lines in the calling script, but you don't have to create an XML file into which to put the script. This technique is discussed in the Sesame Script column "Functions, Subroutines, and How to Call Them From Other Scripts."

Creating Script Components

We’re going to touch on the highlights of creating a Windows Script Component file. But for the full monty, we refer you to the Windows Script Component documentation on MSDN, which walks you through the process of creating and using script components and provides reference documentation.

To start creating your .wsc file, there's a convenient tool called Windows Script Component Wizard that's a free download from MSDN. It presents a series of questions and then creates a skeleton .wsc file based on your answers. It also provides you with a globally unique identifier (GUID), which COM requires as a class identifier if you are going to register your component.

The file contains:

  • Information needed for registering the component, including its GUID and the programmatic ID (progID) that can be used to call it in scripts

  • A list of public methods (with their parameters), properties and events exposed by the component

  • The script code that implements these methods, properties and events.

Listing 1 shows the code for a component, which you can copy and paste into a file. Our example script in Listing 2 assumes the file path is c:\scripts\wsc\files-fso.wsc. An explanation follows.

Listing 1: Files-fso.wsc - ScriptingGuys.FSO.FileOperations.WSC component file



<?xml version="1.0"?>

<package>

<component id="ScriptingGuys.FSO.FileOperations.WSC">

  <comment>
    This component enables scripts to call procedures that use the 
    FileSystemObject, part of Script Runtime, to perform text file operations:
    reading from, writing to and copying.
  </comment>

<?component error="true" debug="true"?>

<registration
  description="ScriptingGuys FileSystemObject File Operations Components"
  progid="ScriptingGuys.FSO.FileOperations.WSC"
  version="1.00"
  classid="{052cb1e5-6b07-4f5c-abed-9c3f7e2cc31b}"
  remotable="True">

  <script language="VBScript">
  <![CDATA[

    strComponent = "ScriptingGuys FileSystemObject File Operations Components"

'******************************************************************************

    Function Register
      MsgBox strComponent & " - Windows Script Component registered."
    End Function

'******************************************************************************

    Function Unregister
      MsgBox strComponent & " - Windows Script Component unregistered."
    End Function

'******************************************************************************

  ]]>
  </script>

</registration>

<public>

  <method name="ReadTextFile">
    <parameter name="strInputFile"/>
  </method>
  <method name="WriteTextFile">
    <parameter name="strFileName"/>
    <parameter name="strOutput"/>
  </method>
  <method name="CopyFile">
    <parameter name="strSource"/>
    <parameter name="strTarget"/>
  </method>

</public>

<script language="VBScript">
<![CDATA[

'******************************************************************************

Function ReadTextFile(strInputFile)
'Reads text file and returns array with one element for each line.
'On error returns string with error message.

On Error Resume Next

Const FOR_READING = 1
Dim arrLines()

Set objFSO = CreateObject("Scripting.FileSystemObject")
If Not objFSO.FileExists(strInputFile) Then
  ReadTextFile = "Input text file " & strInputFile & " not found."
  Exit Function
End If

Set objTextStream = objFSO.OpenTextFile(strInputFile, FOR_READING)
If Err <> 0 Then
  ReadTextFile = "Unable to open input text file " & strInputFile & vbCrLf & _
   "Error: " & Err.Number & vbCrLf & Err.Description
  Err.Clear
ElseIf objTextStream.AtEndOfStream Then
  ReadTextFile = "Input text file " & strInputFile & " is empty."
Else
  Do Until objTextStream.AtEndOfStream
    intLineNo = objTextStream.Line
    ReDim Preserve arrLines(intLineNo - 1)
    arrLines(intLineNo - 1) = objTextStream.ReadLine
  Loop
  ReadTextFile = arrLines
End If

objTextStream.Close

End Function

'******************************************************************************

Function WriteTextFile(strFileName, strOutput)
'Writes or appends data to text file.
'On success returns 0, on failure returns error message.

On Error Resume Next
Const FOR_APPENDING = 8
Set objFSO = CreateObject("Scripting.FileSystemObject")
If objFSO.FileExists(strFileName) Then
  Set objTextStream = objFSO.OpenTextFile(strFileName, FOR_APPENDING)
Else
  Set objTextStream = objFSO.CreateTextFile(strFileName)
End If
If Err = 0 Then
  objTextStream.WriteLine strOutput
  WriteTextFile = 0
Else
  WriteTextFile = "Unable to open text file " & strFileName & vbCrLf & _
   "Error: " & Err.Number & vbCrLf & Err.Description
  Err.Clear
End If
objTextStream.Close

End Function

'******************************************************************************

Function CopyFile(strSource, strTarget)
'Copies a file from one location to another and handles errors.
'If target folder does not exist, creates it.
'Overwrites existing file unless it is read-only.
'Remote source or target can be specified with UNC share, e.g., \\host\share

On Error Resume Next
Set objFSO = CreateObject("Scripting.FileSystemObject")
If Not objFSO.FileExists(strSource) Then
  CopyFile = 1
  Exit Function
End If
If Not objFSO.FolderExists(strTarget) Then
  objFSO.CreateFolder(strTarget)
End If
If Err = 0 Then
  objFSO.CopyFile strSource, strTarget & "\"
  If Err = 0 Then
    CopyFile = 0
  Else
    CopyFile = 3
  End If
Else
  CopyFile = 2
End If

End Function

'******************************************************************************

]]>
</script>

</component>

</package>



We used the wizard to create a skeleton .wsc file and GUID for this example. Then we changed some of the default parameters that the wizard created for us. We also added other code, including the functions, that the wizard doesn't include in its template. You can also create .wsc files without the wizard, as they are simply text files. But if you do and you plan to register it, you must obtain a GUID from some other source.

If your organization decides to use script components as part of its scripting environment, it's a good idea to standardize on naming conventions for the progID, component ID and file location for the .wsc files. For example, we've used the same name for both the progID and the component ID: "ScriptingGuys.FSO.FileOperations.WSC". To keep within this convention, for other components we would use other names beginning with "ScriptingGuys." and ending with ".WSC".

The top-level <package> element can contain more than one <component> element, but this file uses only one. The <component> section includes an attribute containing the ID of the component (which, as we mentioned, is the same name we used for the progID). Next comes an optional <comment> element describing the component and a <?component?> element that turns on error-handling and debugging, which are turned off by default.

The rest of the <component> section, which ends with the </component> tag near the end of the file, contains all the other elements for this component: <registration>, <public> and <script>.

Within the <registration> section are attributes specifying the progID and GUID (classid). If you are not going to register the component, the line that specifies the GUID is not required.



classid="{052cb1e5-6b07-4f5c-abed-9c3f7e2cc31b}"



But if you've used the wizard to create the file and the GUID, it makes more sense to leave it in case you later decide to register the component.

Even if the component is not registered, however, the line setting the progID seems to be required.



progid="ScriptingGuys.FSO.FileOperations.WSC"



A test version of the .wsc without this line caused an error when called from a script that used the moniker and GetObject, even though the progID was not used in the script.

The <registration> section also containes description, version and remotable attributes. Setting remotable to "True" enables the component to be created and called on a remote computer.

Note: The wizard does not insert the remotable attribute, but the documentation shows an example using the code:



remotable=true



We found that this threw an error. But we solved the problem by putting True in quotation marks:



remotable="True"




In this same section, we also included optional brief scripts that run when the component is registered or unregistered to announce that this has happened. When we include any script code in the XML file, it has to be within a <script> element that in turn encloses a CDATA element:



<script language="VBScript">
  <![CDATA[
    'Script code here.
  ]]>
  </script>



The CDATA element tells XML parsers that the code within it should not be treated as XML.

The <public> element exposes three methods with their parameters:

Method

Parameters

ReadTextFile

strInputFile

WriteTextFile

strFileName
strOutput

CopyFile

strSource
strTarget


The code for each of these methods is contained in separate functions in the <script> section. The method and parameter names listed in the <public> section must match the names of the functions and their parameters in the <script> section. The <public> section doesn't provide a way to specify what kind of values each method returns, so we describe them in comments at the beginning of each function.

The <script> section takes the form of separate functions or subroutines (we've used only functions in this example), also enclosed in a CDATA element. It can also include code for properties and events, but we haven't used them here (see the Windows Script Components documentation on MSDN for property and event code examples).

The three functions, ReadTextFile, WriteTextFile and CopyFile, are prototypes. They work, but they may not be the best way to accomplish these tasks for your particular organization and scripting environment. As always with our code examples, take them as starting points to adapt to your own needs and customize to your own tastes. Their main purpose here is to illustrate a practical use for script components.

All three functions use the FileSystemObject object model, part of the Script Runtime. For copying files, it's also possible to use WMI classes such as CIM_DataFile and Win32_Directory, so if FSO doesn't do exactly what you want to do you may want to experiment with these.

A particular issue in writing procedures for inclusion in .wsc files is that the component procedures can't use WScript.Echo or WScript.StdOut.Write to display output. The component is not itself a script, so it doesn't run within the WSH scripting environment and can't take advantage of these output methods. Consequently, the procedures in this component return output information to the calling script for display or interpretation.

All the functions check for errors and return error messages explaining them. But the functions use different strategies for return values.

The ReadTextFile function takes advantage of VBScript's chameleon-like variable type, variant. The function returns an array of strings if it succeeds, but a string with an error message if it fails. The calling code must check the return value type and handle it accordingly. (This is demonstrated later in Listing 2.) VBScript is weakly typed, as opposed to strongly typed system-level programming languages such as C++ or Visual Basic. So it lets us get away with effectively treating return values as different types depending on what we find in them.

The WriteTextFile function appends a string to a text file, and returns an error string that can be checked and displayed by the calling script. CopyFile, on the other hand, returns an integer value representing different outcomes: the calling script has to do the work of checking the integer returned, taking appropriate action, and displaying a corresponding message.

Calling a Script Component in a Script

Now you've got yourself a shiny new Windows Script Component. But that was just the setup: the punchline is calling it from a script. Before you can do that, though, you have to either register the component or place it in a specific directory and call it from there.

The simplest approach is to put the .wsc file into a specific directory. Then, without having to register the COM object, you can connect to it using a moniker. You just have to be sure that the .wsc file is in the expected directory on any machine on which you call the component. If you decide to use this method, you may want to standardize on a directory for your organization. We usually use c:\scripts as the working directory for our script examples, so here we use c:\scripts\wsc for script components.

If you've written any WMI scripts, you have probably used a moniker. Non-scripters may think of a moniker as something like a nickname, and that's not too far off in the COM world either. To bind to WMI using a moniker, you use a line of code something like this:



Set objWMIService = GetObject("winmgmts:")



That "winmgmts:" is the WMI moniker, and you have to use GetObject rather than CreateObject to instantiate it.

With Windows Script Components you use the moniker "script:" followed by the full path to the .wsc file. You could also use a URL to the .wsc file if it were available on a Web server. The Windows Script Components runtime, Scrobj.dll, is already registered on machines running Windows and it recognizes the "script:" moniker.

For example, if the ScriptingGuys.FSO.FileOperations.WSC component is not registered we can connect to it using the moniker followed by the path to its file:



Set objFilesFso = GetObject("script:c:\scripts\wsc\files-fso.wsc")



Then using the object reference, objFilesFso, we can call the methods of our object, as we'll see in Listing 2.

If we want to register the component object, that requires one more step. We have to run the system command-line tool regsvr32.exe on all the machines where we want to use it. For our component, the command line would look like this:



regsvr32 file:\\c:\scripts\wsc\files-fso.wsc



Once we have done this, we can get an object reference to our object using CreateObject (rather than GetObject) and the progID (rather than the path to the .wsc file):



Set objFilesFso = CreateObject("ScriptingGuys.FSO.FileOperations.WSC")



Only this line will be different; the rest of the script will be the same.

We've specified remotable="True" in the <registration> element of the component. This means that we should be able to call the component remotely if the component:

  • is registered on the local machine where the script is running.

  • is registered and the .wsc file is present on the remote machine specified in the script.

To call a remote script component, we specify the name of the remote machine (sea-wks-1 in this example) where the component is registered and the file is present as the second parameter of CreateObject:



Set objFilesFso = CreateObject("ScriptingGuys.FSO.FileOperations.WSC", _
 "sea-wks-1")



We can't do this with the moniker because GetObject does not accept the name of a remote machine as a second parameter.

Note: As with all remote scripting, the script must run with credentials that have Administrator privileges on the local and remote machines. Calling the component remotely may also require configuration of DCOM remoting with the Component Services snap-in, under Administrative Tools in Control Panel.


This remoting capability is probably not critical for the functions in the component we’ve created here. In its functions, FileSystemObject lets us use UNC paths to remote shares, such as \\server\public, as parameters, allowing us to copy files between machines.

With other COM objects that do not contain intrinsic remoting in their procedures, however, the remoting capability added by wrapping the code in a Windows Script Component could prove handy. We haven't experimented much with this option, however, so we're not sure how well it works.

In this example script we'll take advantage of each of the three functions in the component. We call each function as a method of the objFilesFso object. The parameters we pass in must match the number, order and types of parameters exposed by the procedure in the script component. We also have to know what return values to expect back and handle them in the calling script. For example:



intCopy = objFilesFso.CopyFile(strItem, strTargetFolder)



returns an integer, as we've indicated with the name of the variable that receives it, intCopy. We interpret the integer with a Select Case structure.

Listing 2 creates an object reference to files-fso.wsc with the "script:" moniker. Then it gets a list of files from a text file and copies them to another folder, logging the results to another text file. The input text file, filelist.txt in this example, must contain the full path to an existing file on each line, for example:



c:\scripts\file1.txt
c:\scripts\file2.doc
c:\scripts\file3.xls



Listing 2: Copyfiles.vbs - Copy files to a folder.



'If no path specified, file must be in same directory as script.
'For remote path or folder, use UNC share name, e.g., \\sea-srv-1\public
strInputFile = "filelist.txt" 'Each line must be full path of file to copy.
strOutputFile = "copylog.txt"
strTargetFolder = "c:\scripts-test"

'Bind to WSC with moniker.
Set objFilesFso = GetObject("script:c:\scripts\wsc\files-fso.wsc")

'Read contents of text file.
'If success, returns array. If failure, returns string with error message.
varText = objFilesFso.ReadTextFile(strInputFile)
If IsArray(varText) Then
  strCopy = vbCrLf & "Files copied " & Now
  For Each strItem In varText
    strCopy = strCopy & vbCrLf & vbCrLf & "File: " & strItem
    intCopy = objFilesFso.CopyFile(strItem, strTargetFolder)
    Select Case intCopy
      Case 0
        strCopy = strCopy & vbCrLf & "  Copied to folder " & strTargetFolder
      Case 1
        strCopy = strCopy & vbCrLf & "  ERROR: File not found"
      Case 2
        strCopy = strCopy & vbCrLf & "  ERROR: Unable to create folder " & _
         strTargetFolder & vbCrLf & Err.Number & " " & Err.Description
        Err.Clear
      Case 3
        strCopy = strCopy & vbCrLf & _
         "  ERROR: Unable to copy file to folder " & strTargetFolder & _
         vbCrLf & Err.Number & " " & Err.Description
        Err.Clear
      Case Else strCopy = strCopy & vbCrLf & _
       "  ERROR: Unable to determine outcome of file copy operation"
    End Select
  Next
Else
  WScript.Echo varText
  WScript.Quit
End If

'Display and write copy log to text file.
WScript.Echo strCopy
strWrite = objFilesFso.WriteTextFile(strOutputFile, strCopy)
If strWrite <> "Success" Then
  WScript.Echo strWrite
End If



There are plenty of other potential ways to use the functions in this component. For example, you could use ReadTextFile to get a list of remote machines from a text file. And you could use WriteTextFile to log the output of just about any script.

Post-Script

With Windows Script Components, we've found a way built into Windows scripting technologies to encapsulate reusable code in an XML file that you can use as a COM server. This lets you package your most useful code snippets and procedures and make them available to all your scripts with very little coding overhead.

We kid you not.

Doctor Scripto

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