How can I pipe from Get-Content -Wait? - powershell

Question

I would like to pipe the output of Get-Content $file -Wait to a custom PowerShell script. The script looks like this.
$lines = ($input | Out-String) -replace "`r", "" -split "`n"
foreach ($line in $lines) {
#Process $line
Write-Host $line
}
Basically the idea is to take the input, format it nicely and then process the output before it gets printed to the console.
The problem is nothing is getting sent to my script when I call it like cat $file -Wait | MyScript. If I do cat $file -Wait or cat $file | MyScript, everything works as expected. But combining the pipe and the wait parameter doesn't work.
Is there some syntax I need to use to allow processing the -Wait parameter? I tried using Out-String -Stream, but that doesn't work either.

Answer 1

The problem is with $input.
If you do this :
Get-Content $file -Wait | Get-Member -InputObject $input
Or
Get-Content $file -Wait | Get-Member -InputObject $_
You will get :
Get-Member : The input object cannot be bound to any parameters for the command either because the command does not take pipeline input or the input and its properties do not match any of the parameters that take pipeline input.
If Get-Member is unable to read the object going through the pipeline, you know that something is very wrong with the object (or the pipelining).
Let's try piping $input to Out-String, like you are doing in your script :
Get-Content $file -Wait | Out-String $input
You will get :
Out-String : A positional parameter cannot be found that accepts argument 'System.Collections.ArrayList+ArrayListEnumeratorSimple'.
At line:1 char:52
+ get-content '.\netstat anob.txt' -wait | Out-String <<<< $input
+ CategoryInfo : InvalidArgument: (:) [Out-String], ParameterBindingException
+ FullyQualifiedErrorId : PositionalParameterNotFound,Microsoft.PowerShell.Commands.OutStringCommand
So, indeed, "Get-Content" -Wait gives you a weird kind of object : a System.Collections.ArrayList+ArrayListEnumeratorSimple .
It looks like it's the result of the GetEnumerator() method from a System.Collections.ArrayList object, or something like that.
Given the fact that Get-Member or even "Get-Member -Force" is unable to read this kind of "Object", from Powershell's point of view, it's not a object.
The workaround would be to drop the -Wait parameter from Get-Content and find another way of achieving what you want, possibly by running Get-Content and then, running "Get-Content -Tail 1" several times in a loop.

Answer 2

This is possible if your script accepts pipeline input. You can see it as you have mentioned when you pipe to other cmdlets like Select-String. For example defining script.ps1 as:
process { Write-Host "line: $input" }
Then running
1..200 | foreach { add-content -Path test.txt -Value "$_"; start-sleep 1 }
in one PowerShell session and
gc test.txt -wait | .\script.ps1
in another, you can see that each line is piped to the script.

Answer 3

I don't see any way to do what you are asking. -Wait initiates a loop that never ends, the only way to stop is to manually kill it. Since it will always be stuck inside the loop anything you try to do after initiating the loop is never going to process.

Answer 4

The problem is in this line:
Write-Host $line
You should use Write-Output instead. Write-Output sends objects to pipeline, Write-Host directly to host (console).