Reputation: 31

PowerShell 'if' condition

Here is a quick little PowerShell blurp that is supposed to get the device's IP address, Service Tag, and MAC address of any active MAC addresses on the device (active meaning there is a connection).

Anyway, if I don't use an if statement, this works perfectly, but if I do, it only executes the first line:

Test-Connection $computername -count 1 | select @{Name="Computername";Expression={$_.Address}},Ipv4Address

If the device is on... and the last line of the device is off.

Write-Host "Device is offline"

Here is my little PowerShell 'script':

$computername = Read-Host 'Enter Computer Name'
$online = Test-Connection -Computername $computername -BufferSize 16 -Count 1 -Quiet
IF ($online -eq "True") {
    Test-Connection $computername -count 1 | select @{Name="Computername";Expression={$_.Address}},Ipv4Address
    Get-WmiObject win32_SystemEnclosure -computername $computername | select serialnumber
    Get-wmiobject -class "Win32_NetworkAdapterConfiguration" -computername $computername |Where{$_.IpEnabled -Match "True"}
} Else {
    Write-Host "Device is offline"
}

Why does this happen? What might I be doing wrong?

Upvotes: 3

Answers (3)

JohnLBevan

Reputation: 24410

Try this:

$computername = Read-Host 'Enter Computer Name'
$online = Test-Connection -Computername $computername -BufferSize 16 -Count 1 -Quiet
IF ($online -eq $true) {

    Write-Host "Device is online"
    Test-Connection $computername -count 1 | select @{Name="Computername";Expression={$_.Address}},Ipv4Address

    try {
        [PSObject[]]$systemEnclosures = Get-WmiObject win32_SystemEnclosure -computername $computername -ErrorAction Stop
        Write-Host "Found $($systemEnclosures.Count) System Enclosures"
        $systemEnclosures | select serialnumber
        [PSObject[]]$NetworkAdapterConfiguration = Get-wmiobject -class "Win32_NetworkAdapterConfiguration" -computername $computername -ErrorAction Stop
        Write-Host "Found $($NetworkAdapterConfiguration.Count) Network Adapter Configurations"
        $NetworkAdapterConfiguration = $NetworkAdapterConfiguration | Where{$_.IpEnabled}
        Write-Host "Found $($NetworkAdapterConfiguration.Count) IP Enabled Network Adapter Configurations"
        $NetworkAdapterConfiguration
    } catch {
        Write-Host "An Error Occurred"
        Write-Host $_.ToString() #show exception info
    }
} Else {
    Write-Host "Device is offline"
}

NB: I'm not suggesting you keep this code in your final script; just use this to understand what's happening behind the scenes.

Per comments; use $true instead of "true", as though both are truthy, using the wrong type will lead to a false understanding of the language / some really odd bugs down the line where you find that lines like if($true -eq "false") {write-output "Well, this is unusual"} will cause some odd behaviour.

Also you may wish to look into replacing Write-Host with Write-Output for any logical return values, or Write-Verbose/Write-Debug for any informative/investigation outputs; then call the code with the appropriate switches / preferences... but that's unrelated to your issue. More on that is in Write-Host Considered Harmful.

Update

Per comments, the issue you're seeing is a ~~bug~~ gotcha: https://github.com/PowerShell/PowerShell/issues/4552

If the data coming out of this code is just to be displayed in the console, you can avoid this issue by explicitly calling the Format-Table command:

$computername = Read-Host 'Enter Computer Name'
IF (Test-Connection -Computername $computername -BufferSize 16 -Count 1 -Quiet) {
    Test-Connection $computername -count 1 | select @{Name="Computername";Expression={$_.Address}}, 'Ipv4Address' | Format-Table
    Get-WmiObject win32_SystemEnclosure -computername $computername | select serialnumber | Format-Table
    Get-wmiobject -class "Win32_NetworkAdapterConfiguration" -computername $computername | Where{$_.IpEnabled} | Format-Table
} Else {
    Write-Host "Device is offline"
}

If you need the output to go to the pipeline for consumption elsewhere, all's good as it is (i.e. without the format-table piece); the objects are being correctly written to the pipeline; the issue is simply that when it comes to displaying all of the results together, the first object causes PowerShell to create columns ComputerName and Ipv4Address, and PowerShell subsequently attempts to display those properties of the following objects, despite those not having such properties. That said, this could be improved by putting the different object types into different properties of a custom object for easy reference. For example,

$computername = Read-Host 'Enter Computer Name'
If (Test-Connection -Computername $computername -BufferSize 16 -Count 1 -Quiet) {
    (new-object -TypeName PSObject -Property @{
        ConnectionTest = Test-Connection $computername -count 1 | select @{Name="Computername";Expression={$_.Address}}, 'Ipv4Address'
        SystemEnclosures = Get-WmiObject win32_SystemEnclosure -computername $computername | select serialnumber
        NetworkAdapterConfigs = Get-wmiobject -class "Win32_NetworkAdapterConfiguration" -computername $computername | Where{$_.IpEnabled}
    })
} Else {
    Write-Host "Device is offline"
}

Upvotes: 2