Powershell regex to get DC from Distinguished Name - regex

Question

I'm trying to get the first DC that appears for a given Distinguished name as below:
CN=blah1,CN=Computers,DC=blah2,DC=blah3
So in plain English I wish to "replace all strings, up to 'DC=', and return any value from DC= and up to the next ,
I've tried working it out using online calculators but somehow doesn't work.

Answer 1

Have a look at this:
$str = "CN=blah1,CN=Computers,DC=blah2,DC=blah3"
$str -match '^.*?(DC=.*?),'
$Matches[1] # DC=blah2
It finds the first DC=* where * is whatever follows the = until the next comma.

Answer 2

Well to show the second easy method to grep certain parts of your string. Try to use - split:
$string = "CN=blah1,CN=Computers,DC=blah2,DC=blah3"
#Seperate the string at ",DC=" and get the second part
($string -split ',DC=')[1]
Returns: blah2

Answer 3

I think the best (by "best" I mean the "most robust") answer is not to do string parsing or a regex in the first place and use the IADSPathname interface to retrieve the part of the name you're interested in. This is available (albeit initially somewhat complex) in PowerShell via the Pathname COM object. The Pathname object handles all escaping of characters automatically.
Example:
$ADS_SETTYPE_DN = 4
$ADS_DISPLAY_VALUE_ONLY = 2
$Pathname = New-Object -ComObject Pathname
$distinguishedName = "CN=blah1,CN=Computers,DC=blah2,DC=blah3"
# Set the AD path in the object
$Pathname.GetType().InvokeMember("Set", "InvokeMethod", $null, $Pathname, #($distinguishedName,$ADS_SETTYPE_DN))
# Get the number of name elements
$numElements = $Pathname.GetType().InvokeMember("GetNumElements", "InvokeMethod", $null, $Pathname, $null)
# Retrieve the second-to-last name element (outputs "DC=blah2")
$Pathname.GetType().InvokeMember("GetElement", "InvokeMethod", $null, $Pathname, $numElements - 2)
# Set the display type to values only
$Pathname.GetType().InvokeMember("SetDisplayType", "InvokeMethod", $null, $Pathname, $ADS_DISPLAY_VALUE_ONLY)
# Retrieve the second-to-last name element (outputs "blah2")
$Pathname.GetType().InvokeMember("GetElement", "InvokeMethod", $null, $Pathname, $numElements - 2)
Admittedly, the Pathname COM object is not easy to use in PowerShell because you have to call it indirectly. This can be alleviated somewhat by using a "wrapper" function to invoke the object's methods. Example:
$ADS_SETTYPE_DN = 4
$ADS_DISPLAY_VALUE_ONLY = 2
$Pathname = New-Object -ComObject Pathname
function Invoke-Method {
param(
[__ComObject] $object,
[String] $method,
$parameters
)
$output = $object.GetType().InvokeMember($method, "InvokeMethod", $null, $object, $parameters)
if ( $output ) { $output }
}
$distinguishedName = "CN=blah1,CN=Computers,DC=blah2,DC=blah3"
# Set the AD path in the object
Invoke-Method $Pathname "Set" #($distinguishedName,$ADS_SETTYPE_DN)
# Get the number of name elements
$numElements = Invoke-Method $Pathname "GetNumElements"
# Retrieve the second-to-last name element (outputs "DC=blah2")
Invoke-Method $Pathname "GetElement" ($numElements - 2)
# Set the display type to values only
Invoke-Method $Pathname "SetDisplayType" $ADS_DISPLAY_VALUE_ONLY
# Retrieve the second-to-last name element (outputs "blah2")
Invoke-Method $Pathname "GetElement" ($numElements - 2)
For a complete solution, I wrote a PowerShell module called ADName that provides an easy-to-use interface for both the Pathname and the NameTranslate objects.
In the ADName module, the Get-ADName cmdlet is a wrapper for the Pathname object, and the Convert-ADName cmdlet is a wrapper for the NameTranslate object. Example:
# Get elements of name as an array
$nameElements = Get-ADName "CN=blah1,CN=Computers,DC=blah2,DC=blah3" -Split
# Output second-to-last element (e.g., "DC=blah2")
$nameElements[-2]
# Get name elements (values only)
$nameElements = Get-ADName "CN=blah1,CN=Computers,DC=blah2,DC=blah3" -Split -ValuesOnly
# Output second-to-last element (e.g., "blah2")
$nameElements[-2]
I've found that the Get-ADName and Convert-ADName cmdlets are extremely useful in a variety of scenarios. One example:
$name = "CN=blah1,CN=Computers,DC=blah2,DC=blah3"
# Output canonical name of parent path; e.g.: "blah2.blah3/Computers"
$name | Get-ADName -Format Parent | Convert-ADName Canonical

Answer 4

Split is enough for this, i.e:
$s = "CN=blah1,CN=Computers,DC=blah2,DC=blah3"
$s.Split(",")[2].Split("=")[1]
# blah2
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