Scripting Groups with the VBScript ‘Join’ Command
This ezine will help you decide the best strategy for controlling a user’s environment based on group membership. We will examine the use of the ‘Join’ command in VBScript and also discuss alternatives such as Group Policy. I thank Charles Trevor for supplying the idea and the example script.
- This Week’s Secret
- Primary problem with interrogating memberOf
- Scripting Techniques
- This Week’s Mission
- Example 1: Script to Display the Group(s) that a User is memberOf
- Learning Points for the ‘Join’ Command
Avoid groups. This is indeed strange advice for an article on scripting group membership. Nevertheless, my recommendation remains to research such as a group policy before you start writing VBScript commands. After all, think of that name, why is it called GROUP policy, not User Policy? Even in cases where there is no suitable group policy, with a little lateral thinking you may be able to find a workaround and thus avoid needing to control a script through group membership.
OK, perhaps this talk of alternatives to scripting groups is unrealistic. I accept reluctantly that there are occasions where you really do need to extract a user’s group membership in your VBScript. The main technical problem is that unlike other LDAP properties, memberOf (group membership) can have multiple values. All the groups to which a user belongs are stored in an array. In my opinion, data held in arrays is an order of magnitude more difficult for VBScript to extract, than data held in non-array fields. In conclusion, my advice is this, if you decide that your script must determine group membership, then take the time to become an expert at arrays in general, and the ‘Join’ command in particular.
Secondary problem with groups
Here follows a classic case of knowledge is power. In a domain, each user object is a member of the Domain Users group. The problem in scripting occurs because the Domain Users group is their default group, their primary group and also the only group that many users belong. What happens is that when VBScript interrogates a user’s properties, the Domain Users group does not show in the output. It’s as though the operating system knows internally about the Domain Users, but it’s hard for a VBScript to get a handle on this membership information. The final complication is that VBScript needs a different technique to handle a single value held by memberOf, compared with cases where memberOf holds an array of groups.
Our ‘Join Groups’ VBScript is a triumph for researching the subject matter. Another related technique, which I often recommend is the ‘Walk-Through’. If you launch Active Directory Users and Computers and inspect the memberOf property tab, then you can see that the User belongs to the Domain Users. Closer scrutiny reveals that the Domain Users is the primary group. By constantly returning to this memberOf tab, you can understand why your script produces a particular output. If the script does not work as expected, then we can gain extra information by adding other groups to the memberOf tab – then running the script again.
I cannot resist the temptation to preach on my favorite subject: build your script in stages. Today’s script does very little on its own, what we really need is to bolt-on a combination of: GetEx, InStr and MapNetworkDrive commands, only then do have a complete script to solve a variety of network problems.
This Week’s Mission is to produce a scriplet with the dedicated and important job of displaying a user’s group membership. Example 1 holds a self-contained block of code, which is purely designed to display the value(s) held by the LDAP property called memberOf. To be effective in a production script, you would have to add more code. Thus the simplicity of this week’s example is both its strength and its weakness. It works, but only in a limited situation, it cries out for the context of a wider project.
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This script will echo a string containing all the groups to which a user is a member. The idea is to master one command block which you can then employ in other scripts which need to take action depending on group membership.
- Copy and paste the script below into notepad, or get a script editor such as OnScript.
- Save the file with .vbs extension e.g. JoinGroup.vbs
- I recommend that you investigate Active Directory Users and Computers to check the current user’s group membership. If necessary add the current user to more groups, then run the script a second time.
‘ Example VBScript to interrogate group membership
‘ Authors Charles Trevor and Guy Thomas
‘ Version 2.2 – April 2007 http: //computerperformance.co.uk
Dim strGroups, colGroups
Dim objUser, CurrentUser
Set objUser = CreateObject("ADSystemInfo")
Set CurrentUser = GetObject("LDAP://" & objUser.UserName)
colGroups = CurrentUser.memberOf
If IsEmpty(colGroups) Then
strGroups = ""
ElseIf TypeName(colGroups) = "String" Then
strGroups = LCase(colGroups)
strGroups = LCase(Join(colGroups))
‘ End of example script.
Note 1: The command ‘Join’ returns a string value. In this example, our variable strGroups is created by concatenating a number of substrings (groups) contained in the array colGroups. Observe how we can trace this array back to CurrentUser.memberOf.
Note 1a: The syntax is: Join(list[, delimiter]). In this example we simplify the expression to: Join(list)
Note 2: Take the opportunity to study how VBScript employs the Set, GetObject and CreateObject methods.
Note 3: I love ‘If’ statements. The power of this particular ‘If.. Then…Else’ block is that caters for users in all situations. If a user is only a memberOf one group, LCase(colGroups) takes care of business. Else the famous ‘Join’ command copes for users with multiple group membership.
Note 4: There are lots of interesting properties in this script, for example, .memberOf and .UserName.
Note 5: In many scripts, groups and ‘Join’ require the value to be in lower case, hence Lcase(Join(colGroups). That said, on my machine the script worked without Lcase, nevertheless, watch out for case-sensitivity with groups and with ‘Join’.
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Summary of Scripting Groups with ‘Join’
I guess if you have got this far, then you really need to master this technique of scripting group membership. However, I will make one last plea: if you get nothing but error messages and frustration, then think laterally, and particularly, think ‘Group Policy will be my salvation’.
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