Powershell indexing for creating user logon name - powershell

Question

I'm trying to make a user creation script for my company to make things more automated.
I want the script to take the Firstname + Lastname[0] to make the users logon name, but i can't get the syntax right,
I have tried writing {} and () but no luck there.
that's the original peace from my script
New-ADuser...........-UserPrincipalName $fname+$lname[0]
any tips?

Answer 1

Gabriel Luci's helpful answer provides an effective solution and helpful pointers, but it's worth digging deeper:
Your problem is that you're trying to pass expression $fname+$lname[0] as an argument, which requires enclosing (...):
New-ADuser ... -UserPrincipalName ($fname+$lname[0])
PowerShell has two distinct parsing modes, and when a command (such as New-ADUser) is called, PowerShell operates in argument mode, as opposed to expression mode.
Enclosing an argument in (...) forces a new parsing context, which in the case of $fname+$lname[0] causes it to be parsed in expression mode, which performs the desired string concatenation.
In argument mode, unquoted arguments are implicitly treated as if they were enclosed in "...", i.e., as expandable strings under the following circumstances:
If they don't start with (, #, $( or #(.
If they either do not start with a variable reference (e.g., $var) or do start with one, but are followed by other characters that are considered part of the same argument (e.g., $var+$otherVar).
Therefore, $fname+$lname[0] is evaluated as if "$fname+$lname[0]" had been passed:
The + become part of the resulting string.
Additionally, given that inside "..." you can only use variable references by themselves (e.g., $fname), not expressions (e.g., $lname[0]), $lname[0] won't work as intended either, because the [0] part is simply treated as a literal.
Embedding an expression (or a command or even multiple expressions or commands) in "..." requires enclosing it in $(...), the subexpression operator, as in Gabriel's answer.
For an overview of PowerShell's string expansion rules, see this answer.
The following examples use the Write-Output cmdlet to illustrate the different behaviors:
$fname = 'Jane'
$lname = 'Doe', 'Smith'
# WRONG: Same as: "$fname+$lname[0]", which
# * retains the "+"
# * expands array $lname to a space-separated list
# * treats "[0]" as a literal
PS> Write-Output -InputObject $fname+$lname[0]
Jane+Doe Smith[0]
# OK: Use an expression via (...)
PS> Write-Output -InputObject ($fname+$lname[0])
JaneDoe
# OK: Use an (implicit or explicit) expandable string.
PS> Write-Output -InputObject $fname$($lname[0]) # or: "$fname$($lname[0])"
JaneDoe
# OK: Use an intermediate variable:
PS> $userName = $fname + $lname[0]; Write-Output -InputObject $userName

Answer 2

Use a string for the UserPrincipalName, with the variables in the string:
New-ADuser -UserPrincipalName "$fname$($lname[0])"
PowerShell can usually figure out when you put a variable inside a string. When it can't, like in the case of $lname[0], you enclose it in $().
This is called "variable expansion" (other languages, like C#, call it "string interpolation"). Here's a good article that describes it in more detail: https://powershellexplained.com/2017-01-13-powershell-variable-substitution-in-strings/

Answer 3

i just saw the answers and a minute before i realized that i should actually set it up as another variable, $logon = $fname+lname[0]
and pass it as -userPrincipalName $logon.
Thanks for the help, you guy are the best!