Wednesday, August 26, 2009

Add a List of Users to the Local Admins Group

Just a quick update here, and another real-world example of where the Split() method of a string can come in handy for day-to-day tasks.

Today I had to add a list of about 20 individual usernames as administrators to a particular machine. Someone sent me the comma-separated list in an IM, and it took me about ten seconds:

PS> 'user1,user2,user3,user4,user5,user6,user7,user8,user9,user10'.split(',') |
>> %{net localgroup administrators $_ /add}

The command completed successfully.

The command completed successfully.

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Wednesday, August 12, 2009

Use PowerShell to Get Local Group Members from a Remote Computer

I had a friend ask me recently how to get a list of administrators from a server.

"That's easy" I thought. "You just have to... um... actually..."

It turns out that this can be frustratingly difficult in PowerShell, so I wrote this module to make it easier when I'll need to do this in the future. It's comprised of three functions:
  • Add-NoteProperty: About 90% of the time when I want to create a custom PSObject and add some properties, they're all NoteProperties. This function makes adding a property easy, like so: Add-NoteProperty $my_object 'PropertyName' $property
  • Get-COMProperty: This is a kludgy hack to get around the fact that members of groups gotten through ADSI get returned as __ComObject objects, and you have to call the InvokeMember() static method of the class in order to get at their properties. Now I can just do this: Get-COMProperty $com_object 'PropertyName'
  • Get-LocalGroups: This is the function that we needed. It returns a list of custom PSObjects representing the local groups on a server, and each one has a property called Members that is a list of custom PSObjects for each member, including the Name, Domain, and ADSPath. From there, you can use whatever method you want to the object you want, whether it's using Get-QADUser for domain users, or whatever, for example: Get-LocalGroups computername.
If you're using Powershell v2 CTP3 or higher, you can use help on each of the functions to see examples if you forget. You can download the module from Poshcode.org here.



Saturday, August 8, 2009

String Manipulation: Splitting and Joining Strings

I think it's time to get back to some more basic things, so let's get to it.

The split()method of a string object lets you define a delimiter and "split" the string up into multiple pieces, which are returned as an array.

Let's say I do this:

PS C:\Users\tojo2000> $string = "one two three four"
PS C:\Users\tojo2000> $string.split(" ")
one
two
three
four


As it turns out, though, split() splits on a single whitespace character by default.

Observe:

PS C:\Users\tojo2000> $string = "one two three four six"
PS C:\Users\tojo2000> $string.split()
one
two
three
four

six


What's the practical use for this? Let's say you have a tab-separated values file called people.txt that looks like this:

Doe John California
Doe Jane Texas
Neuman Alfred Nebraska


And you want the output to be First Last, Location. You could do it like so:

PS C:\Users\tojo2000> Get-Content people.txt |
>> %{$data = $_.split("`t"); Write-Output "$($data[1]) $($data[0]), $($data[2])"}
>>
John Doe, California
Jane Doe, Texas
Alfred Neuman, Nebraska


But what if you have a file like this called people2.txt (let's say the first part is some kind of ID)?

2323:Doe John California
827:Doe Jane Texas
982982:Neuman Alfred Nebraska


Now you have two delimiters, but the split() method of a string object takes a string as an argument, so you would have to split twice in order to get each part of the string split into an array. If only there was some way to split on a regular expression... Oh, wait, there is.

PS C:\Users\tojo2000> Get-Content people2.txt |
>> %{$data = [regex]::split($_, '\t|:'); Write-Output "$($data[2]) $($data[1]), $($data[3])"}
>>
John Doe, California
Jane Doe, Texas
Alfred Neuman, Nebraska


('\t|:' is a regular expression for a tab character or a colon)

What if you have an array, and you want to make a string out of it? Then you can join the strings together using join(). Now there are two ways to join a list of strings, depending on whether you're using PowerShell v1 or v2.

The first way works in both v1 and v2:

PS C:\Users\tojo2000> $buncha_strings = 'one', 'two', 'three', 'four', 'five', 'six'
PS C:\Users\tojo2000> [string]::join(' and a ', $buncha_strings)
one and a two and a three and a four and a five and a six


So what practical use would there be? For a completely contrived example, maybe you want to create a new version of people2.txt called people3.txt that uses pipe characters to separate the fields. We'll split the strings up into an array just like before, but then we'll join them back together the way we want them.

PS C:\Users\tojo2000> Get-Content people2.txt |
>> %{$data = [regex]::split($_, '\t|:'); [string]::join('|', $data)} > people3.txt
PS C:\Users\tjo2000> Get-Content .\people3.txt
2323|Doe|John|California
827|Doe|Jane|Texas
982982|Neuman|Alfred|Nebraska


There is one more way that you can join a list of strings, but this method only works in v2: the -join operator. It works the same way as the other join(), but the syntax is slightly different.

For example, here is how you would join a list of strings by tab characters:

PS C:\Users\tojo2000> $list_of_strings -join "`t"


So to wrap this all up, let me give a real-world example. I had a SQL query that I wanted to run that would retrieve the SCCM information for a specific list of computers. I needed to update the list, and I had the computers in a file called machines.txt, with one name per line.

Here's how I slurped up the file to create the new query string:

$query = @"
SELECT * FROM v_R_System
WHERE Netbios_Name0
IN ('{0}')
"@ -f ((Get-Content machines.txt) -join "', '")