Foreach and array variables in powershell

Question

I am importing a CSV and recycling that site based on the values in the CSV. The csv is dynamically buildup based on the alerts we receive. When I try the following code I receive an values printed and errors

import-csv d:\emscripts\recy\recycle.txt -Header "site","IP","Log" | foreach {
    $_.IP
    $_.site
    $appPool = Get-WmiObject -Authentication PacketPrivacy -Impersonation Impersonate  -ComputerName $_.IP -namespace "root/MicrosoftIISv2"  -class IIsApplicationPool | Where-Object {$_.Name -eq "W3SVC/AppPools/$($_.site)" }
    $appPool.Recycle()
    }

*192.168.100.182 Testsite1 You cannot call a method on a null-valued expression. At line:5 char:5 + $appPool.Recycle() + ~~~~~~~~~~~~~~~~~~ + CategoryInfo : InvalidOperation: (:) [], RuntimeException + FullyQualifiedErrorId : InvokeMethodOnNull

192.168.100.131 testsite2 You cannot call a method on a null-valued expression. At line:5 char:5 + $appPool.Recycle() + ~~~~~~~~~~~~~~~~~~ + CategoryInfo : InvalidOperation: (:) [], RuntimeException + FullyQualifiedErrorId : InvokeMethodOnNull*

You can see that the values are printed but it is failing to get anything into the $appPool.

I have changed it to the following and it is working as expected.

    $RecyleSites  = import-csv recycle.txt -Header "site","IP","Log" 
foreach ($site in $RecyleSites)  {
    $site.IP
    $site.site
    $appPool = Get-WmiObject -Authentication PacketPrivacy -Impersonation Impersonate  -ComputerName $site.IP -namespace "root/MicrosoftIISv2"  -class IIsApplicationPool | Where-Object {$_.Name -eq "W3SVC/AppPools/$($site.site)" }
    $appPool.Recycle()
    }

I am trying understand what I am doing wrong in the first set of code ?

Add code to verify that you are really getting back the WMI object that you think you are. — EBGreen
– EBGreen, Commented Feb 10, 2015 at 16:59
Thanks. I did that and I was getting null for $appPool. But the second set of similar code is working. Only difference is I am taking that values in to a array and in the first set I am trying to pass it as I read. I think it is not passing the values of .site or $.IP. — Sunil
– Sunil, Commented Feb 10, 2015 at 17:11
I just tested with ForEach-Object also. No, it is not working, the same result. with the foreach also it is printing the values but not going into Get-WmiObject — Sunil
– Sunil, Commented Feb 10, 2015 at 17:19

Matt · Accepted Answer · 2015-02-10 18:09:21Z

2

I think that this piece of code from your original sample contains your problem:

Where-Object {$_.Name -eq "W3SVC/AppPools/$($_.site)

$_.site isn't in scope any more because $_ now represents the current object in the Where-Object "loop". When you printed $_.site as the first line of the foreach loop, $_ still represented the current item in the $RecycleSite list.

edited Feb 10, 2015 at 18:09

Matt

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answered Feb 10, 2015 at 17:34

campbell.rw

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2 Comments

Sunil Over a year ago

Thanks, I understand what you mean. but how can I use the first loop and the second loop in this case. Any idea ?

campbell.rw Over a year ago

Your corrected version of the code looks OK. Anywhere you can you should explicitly reference the object you want (ie. $site.IP vs $_.IP). The reason to do that is exactly what your question pointed out, that "$_" represents different objects depending where it gets used.

Matt · Accepted Answer · 2015-02-10 17:51:01Z

1

There is a scope issue here for sure. You need to save the variable $_.Site for later use.

$site = $_.site
$appPool = Get-WmiObject -Authentication PacketPrivacy -Impersonation Impersonate  -ComputerName $_.IP -namespace "root/MicrosoftIISv2"  -class IIsApplicationPool | 
    Where-Object {$_.Name -eq "W3SVC/AppPools/$site" }
$appPool.Recycle()

$_ always refers to the object in scope. Saving variables outside of that scope for use is a common practice.

Your ForEach construct is doing just that by saving the assigning the variable in each pass to $site

answered Feb 10, 2015 at 17:51

Matt

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3 Comments

campbell.rw Over a year ago

That's right, which is essentially what he has done by changing to the "foreach($site in $RecycleSites)" loop. But yes, if you want to use the format of the first code snippet, you'd have to do the above.

Sunil Over a year ago

Many thanks, I just got this after checking the question [link] stackoverflow.com/questions/8237251/… and tested it.

Sunil Over a year ago

I am unable to make both answers as answer.. So I am keeping the first answer told me about the issue as answer. Thanks

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