Guy’s Scripting Ezine 59 CONST

Contents for Guy’s Scripting Ezine 59 CONST

• This Week’s Secret – Understanding CONST
• Example 1: Delegating Rights to a Computer
• Summary of CONST

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This Week’s Secret Understanding CONST

When I first started with VBScript, even I just copied and amended other people’s scripts.  However, I could not help but notice that CONST statements always stood out as having a strange aura about them. Naturally, constants by definition do not change, this is what makes CONST fundamentally different from variables.

Since those early days, I have discovered that there are three families of CONSTANTS: system, intrinsic and symbolic constants.  System constants are the easiest to understand, they are constants like, true or false.  Intrinsic constants are built-in constants like vbCr, vbOK and vbCurrency.

Unfortunately, it is the symbolic constants which are widely used in VBScript that are the most difficult to understand.  Here is my view of how how symbolic constants work.  Variable A talks to variable B and variable B talks to variable C.  However A and C cannot talk directly to one another.  So the answer is to change substitute variable B for a symbolic constant.  Let us take an example of a CONST ADS_PROPERTY_APPEND statement which we used to add a member to a group.  The technical explanation of CONST is that because VBScript cannot read from a ‘type library’, we need to employ a symbolic constant instead (Personally I did not find that definition very helpful that is why I evolved my own explanation).

What CONST ADS_PROPERTY_APPEND = 3  is saying to me is this, when VBscript wants to add (APPEND) an Active Directory property (ADS_Property), it has to take the precise form of:  ADS_PROPERTY_APPEND.   Either you just accept that this is how it works, or you delve more deeply and see how the CONST ADS_PROPERTY_APPEND holds the value of 3 throughout the life of the script.  What you cannot do is just substitute 3 for where ever you see ADS_Property.  (Trust me, I tried just substituting 3 for ADS_PROPERTY_APPEND, and the script failed).  What you must do is always script ADS_PROPERTY_APPEND (not 3) when you want to tag on an extra property value.

Here is a roundup what I know about the CONST statement.  VBScript uses symbolic constants, if you do the research, you will discover a whole family of ADS_x_Y constants.  The VBScript procedure is to define these CONST ADS_abc_def at the beginning of your script then call ADS_abc_def when you need to employ the value.  These CONST statements usually refer to an Active Directory property.  Remember that you do not find these CONST statements with network objects such as MapNetworkDrive.

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Example 1 – Delegating Rights to a Computer

VBScript cannot directly modify Active Directory access control lists.  So we have to use the CONST statements to allow the script to make the necessary changes to Active Directory.  It is particularly important to take a minute to work out what this long script will achieve.  The scenario is this: You want to delegate user rights to manage a computer, for example to allow a named user to join this computer to the domain.

Please take the time to investigate the CONST = ADS_ lines in the script

Instructions

1. Copy and paste the script below into notepad.
2. Save the file with .vbs extension e.g. DelegateConst.vbs
3. Double click and then open Active Directory Users and Computers and search the container specified in strContainer.  Did you see a new computer?   Check the security tab, advanced button.  Can you see signs of delegation?
4. Create a computer referenced by strComputer.  Naturally create the computer in strContainer!
5. Important edit: strComputerUser = "guyt".   Change the value to a user in your domain

Guy’s Acknowledgement – this script is heavily based on a Microsoft script.

Learning Points

Note 0:  When troubleshooting make sure that the strComputer, strContainer and strComputerUser are correct.

Note 1: A plain user, strComputerUser = "guyt"  worked for me.  However strComputerUser = "guyt\domain" failed.  I will let you into a secret, something is not quite correct with format of strComputerUser.  The problem is that strComputerUser = "guyt"  keeps generating an Unknown User in the access control list of the security tab.

Note 2: Once the script runs go to Active Directory Users and Computers.  Make sure the security tab is visible by checking the View (Menu), Advanced Features is ticked. right-click the strComputer object, Properties Security (tab), Advanced (Button).  What you see next depends on whether you are using Windows 2000 or 2003, however what you are looking for is evidence of delegation of the rights set by our script.  Tip, scroll down to see the user referenced in the script.

Note 3: Take the time to admire and study all the CONST statements.

Challenges

• Try a different user
• Try to reduce the CONST statements so that they just delegate a few essential user rights.

Summary of CONST

ADS_xyx constants are essential for scripting tasks where you cannot access values directly.  So the technique is to assign the value to a CONST, for example ADS_abc_def = X.  Then call the ADS_abc_def constant at the part of your script where you need to manipulate X.  CONST is just that constant, unchanging, the opposite of a variable.  Technically, VBScript employs symbolic constants when it could not access the type library directly.

See more about VBScript syntax

• VBScripts   • WMI  • Logon Scripts  • Ezine 18 Carriage returns  • Ezine 28 InStr  •Free IP Tracker  • Ezines

• Ezine 47 .put  •Ezine 59 CONST  • Ezine 41 VBS Select case  •Ezine 56 VBS Select case  • Ezine 80 Comspec

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