Retrieve parameters from file - Windows PowerShell - windows

Question

I am writing a super-easy script in PowerShell. The target of this script is to read a list of server names from a txt file and a command block from another txt file. The result of the operation shold be a third txt file containing the information.
Here some code:
cls
$usr = Read-Host "Please insert username, you'll be asked for password later"
$path = Read-Host "Insert a valid path for ServerList.txt file"
$serverList = Get-Content -Path $path | Out-String
$path = Read-Host "Insert a valid path fom Command.txt file"
$commandBlock = Get-Content -Path $path | Out-String
echo "Command: " $commandBlock "will be executed on " $serverList
echo "Press CTRL+Z to abort or"
pause
Invoke-Command -ComputerName $serverList -ScriptBlock { $commandBlock } -credential $usr
Serverlist.txt is a plain text containing something like "server1,server2,server3" and command.txt contain only this "Get-WmiObject Win32_BIOS | Select-Object SerialNumber"
Why the error is Invoke-Command : One or more computer names are not valid. If you are trying to pass a URI, use the -ConnectionUri parameter, or pass URI objects
instead of strings. ?
I even tried to substitute $serverlist with $serverlist.toString() but it's not working. I read somewhere that in this case $serverlist is an Array, how do I do to make everything work?
Consider that https://technet.microsoft.com/en-us/library/hh849719.aspx Invoke-Commands work with "server1,server2,server3" format if you put the string via console.

Answer 1

Your $serverList isn't a list, it's a single string of server1,server2 etc. To make it into an array, you can use -split to split the string by commas.
$serverList = Get-Content -Path $path | Out-String
$serverList = $serverList -split ","

Answer 2

For further understanding of why this doesn't work as you expect, please see the parsing and command syntax help files:
Get-Help about_Parsing
Get-Help about_Command_Syntax
$serverlist
When your text file contains the line server1,server2,server3, this command:
Get-Content -Path .\file.txt | Out-String
Just results in the string server1,server2,server3 and a newline - that's not a valid hostname.
Either format your text file like this (Get-Content automatically splits on line breaks):
server1
server2
server3
or split the string(s) from the file yourself:
$Serverlist = Get-Content -Path $Path | ForEach-Object { $_ -split "," }
$commandblock
For the command block part to work, you can't just drop a string into a ScriptBlock and expect it to execute - you need to recreate it as executable code:
$Code = Get-Content -Path $path -Raw
$CommandBlock = [scriptblock]::Create($Code)
# Now you can do this
Invoke-Command -ScriptBlock $CommandBlock