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.

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