A good question came up in class today while we were
studying PowerShell Format commands. We
took a good look at how Format cmdlets consume the original object and make piping
limited. One of the questions that came
up was if it is possible to save the information to a file and still be able to
use it in the pipeline? Fortunately for
us, there is Tee-Object.
We have a couple of ways that we can implement Tee-Object.
Let’s look at it from a reusability perspective. Here is our starting code:
Get-Process |
Select-Object
-first 3 -Property Name,
VM, PM
And here is the output:
Name VM PM
---- -- --
AcroRd32 472272896 216985600
AcroRd32 132603904
10866688
ApMsgFwd 96550912 1626112
We will now add Tee-Object
and send the data to another cmdlet.
Get-Process |
Select-Object
-first 3 -Property Name,
VM, PM
|
Tee-Object -FilePath C:\PS\Data1.txt
|
Sort-Object
-Property VM
The object was successfully piped to Sort-Object and processed.
We can also read the text file that was created.
PS C:\ps> Get-Content data1.txt
Name VM PM
---- -- --
AcroRd32 472272896 216985600
AcroRd32 132603904
10866688
ApMsgFwd 96550912 1626112
The reusability question now comes into play. What if I needed to use the data that was
sent to the text file in a later operation?
Well, it is now text. That is not
information that we could easily reincorporate into a PowerShell object. Utilizing ConvertTo-CSV and ConvertFrom-CSV
we can. By placing ConvertTo-CSV before
Tee-Object and ConvertFrom-CSV
after Tee-Object was are able to
send a comma separated file to disk.
Get-Process |
Select-Object
-first 3 -Property Name,
VM, PM
|
ConvertTo-CSV
|
Tee-Object -FilePath C:\PS\Data1.csv
|
ConvertFrom-CSV|
Sort-Object
-Property VM
Name VM PM
---- -- --
AcroRd32 132603904 10866688
AcroRd32 472272896 216985600
ApMsgFwd 96550912
1626112
The screen out shows the Sort-Object successfully worked with the object in the PowerShell
pipeline. Import-CSV is also able to successfully
read the object back into member from disk.
PS C:\ps> Import-Csv -Path Data1.csv
Name VM PM
---- -- --
AcroRd32 472272896 216985600
AcroRd32 132603904 10866688
ApMsgFwd 96550912
1626112
Let’s take a look at using the –Variable parameter of Tee-Object.
Get-Process |
Select-Object
-first 3 -Property Name,
VM, PM
|
Tee-Object -Variable Data
|
Sort-Object
-Property VM
Here we removed the –FilePath parameter and added the –Variable
parameter. This is a formal usage of a
variable so we omit the $ in front of the variable name. Here is the contents
of the variable
.
PS C:\ps> $Data
Name VM PM
---- -- --
AcroRd32 472272896 216985600
AcroRd32 132603904
10866688
ApMsgFwd 96550912 1626112
More importantly, here is the object:
PS C:\ps> $Data | Get-Member
TypeName:
Selected.System.Diagnostics.Process
Name
MemberType Definition
----
---------- ----------
Equals Method bool Equals(System.Object obj)
GetHashCode Method
int GetHashCode()
GetType Method type GetType()
ToString Method string ToString()
Name
NoteProperty string Name=AcroRd32
PM
NoteProperty long PM=216985600
VM
NoteProperty long VM=472272896
The information stored in $data is retained as an object.
So the question now comes up as to when to use the –FilePath
parameter and when to use the –Variable parameter. If you will
consume the data that was removed from the pipeline within the same scope of
memory, use the –Variable parameter. If
you will consume the data in another scope of memory, such as another cmdlet or
a different script, the use the –FilePath parameter
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