How do I create an AD username with a dot in it via Powershell?

I'm trying to change an existing script so that my username is firstname intial dot last name for example: John Doe's username will be j.doe Current script works (without the .) as: $firstname.substring(0,$i) + $lastname

thank you.

there are several ways to build that string. [grin] here are 4 of them that come to mind for me.

what the code does ...

• fakes reading in a CSV file with FirstName, LastName data
  replace the entire #region/#endregion block with your preferred data source.
• iterates thru the resulting collection
• builds the desired string with 4 different methods
  my preference is the -f string format operator, but many folks prefer string concatenation.
• sends each out to the display
• adds a divider line between the groups of results

the code ...

#region >>> fake reading in a CSV file
#    when ready to do this for real, use your prefered data source
#    and delete or comment out the entire "#region/#endregion" block
$NameList = @'
FirstName, LastName
Alfa, Bravo
Charlie, Delta
Echo, Foxtrot
'@ -split [System.Environment]::NewLine |
    ConvertFrom-Csv
#endregion >>> fake reading in a CSV file

foreach ($NL_Item in $NameList)
    {
    # string format operator
    '{0}.{1}' -f $NL_Item.FirstName[0], $NL_Item.LastName

    # -join operator
    $NL_Item.FirstName[0], $NL_Item.LastName -join '.'

    # string concatenation
    $NL_Item.FirstName[0] + '.' + $NL_Item.LastName

    # variable-in-string expansion
    "$($NL_Item.FirstName[0]).$($NL_Item.LastName)"

    # yes, you can multiply a string [*grin*] 
    '=' * 20
    }

output ...

A.Bravo
A.Bravo
A.Bravo
A.Bravo
====================
C.Delta
C.Delta
C.Delta
C.Delta
====================
E.Foxtrot
E.Foxtrot
E.Foxtrot
E.Foxtrot
====================

$firstname.substring(0,$i) +"."+ $lastname