PowerShell Tee-Object Cmdlet
The point of Tee-Object is that it can do two thing at once, for example, it could save the output to a file, while redirecting the output to the console.
Think of 'T' as in T-junction, and you will appreciate what this cmdlet can do when you need duplicate outputs.
'Tee' in Windows PowerShell
- Example 1: Eventlog and Tee-Object
- Investigate Parameters of Tee-Object
- Example 2: Tee-Object Saves Data Into Two Files
- Example 3: The Rhythm of the Tee-Object Cmdlet
- Example 4: Tee-Object Sequence Problem
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Example 1: Eventlog and Tee-Object
The scenario: We want to display entries in the System eventlog; furthermore, we want to save these entries into a named file.
# Tee-Object example, trace the branching to $File and Format-Table
Clear-Host
$File = "D:\PShell\EventStuff.txt"
Get-EventLog System -Newest 100 -EntryType Error |
Tee-Object -FilePath $File |
Format-Table TimeGenerated, EventId, Source -AutoSize
Warning: To save disappointment, please modify the value of $File before executing this example on your machine.
Note 1: To see the file contents you could append:
Invoke-Item $File
Note 2: When Tee-Object is the last command in the pipeline, the output is sent to the console.
Challenge: Modify the script to delete all entries with a TimeWritten before 30 days, while keeping a copy of the names of the entries deleted.
Investigate Parameters of Tee-Object
As usual Get-Help reveals useful parameters such as -Append, which would be handy if we wanted the file to keep a record of similar errors over a long period of time.
# Investigate parameters and examples
Get-Help Tee-Object -Full
Note 3: Parameters such as -Variable would be useful in creating other scripts.
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Example 2: Tee-Object Saves Data Into Two Files
One of the commonest jobs for Tee-Object is where you want to save data to files. One file holds the latest results, whereas the other file keeps a running total.
Scenario: You want to save the current eventlog error messages to a file called NewOnly.txt. However, you also want to keep a running total in a file called FullRecord.txt.
# Tee-Object branching with two different files
Function Get-SystemLogRecord {
Param (
[String]$NewOnly = "D:\PShell\NewOnly.txt",
[String]$Continuous = "D:\PShell\FullRecord.txt"
)
Begin {
"Start ….`n"
(Get-Date).ToString()
}
Process{
Get-EventLog System -Newest 100 -EntryType Error
} # Conclusion of function's Process engine
End {
"`n Latest report " + (Get-Date).ToString()
}
} # Function code complete
# Now, here is where Tee-Object uses the Function
Get-SystemLogRecord |
Tee-Object -FilePath $NewOnly |
Out-File $Continuous -append
Invoke-Item $Continuous
If you are not familiar with functions, then here is the bare-bones version of the above script:
$NewOnly = "D:\PShell\NewOnly.txt"
$Continuous = "D:\PShell\Continuous.txt"
Get-EventLog System -Newest 25 -EntryType Error |
Tee-Object -FilePath $NewOnly |
Out-File $Continuous -append
Invoke-Item $Continuous
Note 4: One output goes to -FilePath, and the other branches to Out-File.
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Example 3: The Rhythm of Tee-Object Cmdlet
With Tee-Object you can run a command-line application in PowerShell and have the output both redirected to a file, and displayed on the console. For example:
Clear-Host
$File ="C:\ProgramData\"
Get-ChildItem $File | Tee-Object -FilePath "C:\Temp\TeeProgDat.txt" |
Format-Table Name
Note 5: Observe the rhythm of the command, and understand the position of PowerShell's (|) pipes.
- Input |
- Tee-Object (no pipe yet) 1st output follows directly
- | (pipe after first output)
- 2nd output.
Tee-Object Alias
# Investigate alias
Get-Alias -Definition Tee-Object
CommandType Name ModuleName
—————- —— ———-
Alias tee -> Tee-Object
Incidentally, Tee-Object's alias reminds me of the Tee command in UNIX, which is also used to both store and view the output from another command.
Example 4: Tee-Object Sequence Problem
I find that if you change the sequence after Tee, and try to place the console output BEFORE the file output, then the script fails.
Example A: Problem
# Example A: Failure
Clear-Host
$File ="C:\ProgramData\"
Get-ChildItem $File | Tee Format-Table Name |
-FilePath "C:\Temp\TeeProgDat.txt" -Append
-FilePath : The term '-FilePath' is not recognized as the name of a cmdlet, function, script file, or operable program.
Note 6: There is nothing wrong with using the alias 'Tee' for Tee-Object; as you can see in Example C below. It's the sequence that's the problem.
Example B: Problem. This sequence does not work either:
# Example B: Another failure
Clear-Host
$File ="C:\ProgramData\"
Get-ChildItem $File | Tee | Format-Table Name |
-FilePath "C:\Temp\TeeProgDat.txt" -Append
Example C: Solution. Place the instruction for outputting to the console last.
# Example C: Success!
Clear-Host
$File ="C:\ProgramData\"
Get-ChildItem $File | Tee -FilePath "C:\Temp\TeeProgDat.txt" -Append |
Format-Table Name
Note 7: You could add:
Invoke-Item "C:\Temp\TeeProgDat.txt"
What's new in PowerShell 4.0 ยป
Summary of PowerShell Tee-Object
The purpose of Tee-Object is to act as a 'T' junction in PowerShell's pipe sequence. This means that your script can have two outputs; in the classical example it takes an input and sends one output to a file, and another to the console.
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See more Microsoft PowerShell output tutorials:
• PShell Home • Out-File • Out-GridView • ConvertTo-Csv • ConvertTo-Html • ConvertFrom-Csv
• Tee-Object • Import-CSV • Format-Table • PowerShell Here-String • ConvertFrom-JSON
• Export-CliXml • Format-List • Read-Host • PowerShell Get-History • -f format • Pipe to file
Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.