PowerShell 3.0 Redirection

PowerShell 3.0 New Redirection Commands

From the beginning PowerShell has had the ability to redirect output with | (pipeline), Out-File and the old (>).  Now in PowerShell 3.0 we have the ability to tweak (>) so that we can save warnings and debug information to a text file.

Windows PowerShell 3.0 Redirection Examples


The Redirection Situation in PowerShell 2.0

In addition to my favourite | Out-File, PowerShell supports redirection with the ubiquitous > (greater than symbol).  Let us see an example:

# PowerShell Redirection with >
Get-Process > D:\PShell\Proc0.txt

Note 1: I prefer Get-Process | Out-File D:\PShell\Proc1.txt

Note 2: The double chevron >> means append, whereas the single > means over-write.

Left to its own defaults, PowerShell directs its results to the console.  There are many occasions where you would prefer to save the output as text to be stored in a file.  This page concentrates on the latest redirection techniques.

PowerShell 2.0’s Error Redirection with ‘2>’

Let us be clear, this is a technique for saving errors generated by PowerShell scripts to a file.

There are two keys to getting action:
a) Introduce a non-existent process called xyz, or some such gibberish.
b) The carefully insert 2> and not 2 >.  A space here kills the command.  Also beware of the wrong sequence, this won’t work >2.

# PowerShell’s way of redirecting errors
Get-Process xyz 2> D:\PShell\Proc2.txt

Note 3: A double chevron >> would means append, whereas the single > means over-write.

PowerShell 3.0 Redirection Improvements

PowerShell 3.0 offers the ability to fine-tune redirection by using not only 2>, but also 3> and 4>.  Incidentally, there is also a 1> but I cannot see how it improves on plain >.

Pipeline   1>  (Same as plain >)
Error       2>  (Same as PowerShell 2.0)
Warning  3>
Debug     4>

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More About PowerShell 3.0 Redirection

This is one of those topics where PowerShell provides an ‘About’ help file.  To see more try this:

Get-Help About_Redirection

The Mystery of PowerShell >2&1

Help tells us that we can add errors to the success stream with >2&1.  This is also called merging streams.  However, help appears to leave out a crucial element, you need an initial > to redirect, then PowerShell’s >2&1 at the end thus:

# PowerShell’s way of merging errors
Get-Process svchost > D:\PShell\Proc2.txt  >2&1

Note 4: My mistake was trying Get-Process svchost >2&1 D:\PShell\Proc2.txt

To be fair, I have seen other example:
get-process svchost, powershell 2>&1 | Out-File Svchost.txt

Conclusion: Merging streams with & is not as intuitive as I first thought.

An Alternative to Redirection Commands | Out-File

It could be that I am ‘hard-cooked’, I cannot seem to abandon the habit of using PowerShell’s Out-File; I am finding it hard switching to using these > and >> redirection commands.  Perhaps I don’t generate enough errors to warrant the use of the 2> redirector.

That said, I have filed away in my memory bank the idea of redirection warning messages with 3>.

PowerShell Out-File Example

Get-Service | Out-File D:\Pshell\Services.txt -force

Note 5: Out-File supports switches such as -force that you don’t get with redirection.

See more of what’s new in PowerShell v 3.0 »

Summary of PowerShell 3.0 Redirection

Here is a case where a new PowerShell 3.0 command showed me a technique that I had overlooked in PowerShell 2.0, namely saving errors to a text file.  Another way of looking at PowerShell 3.0’s redirection is that it has now come of age with the introduction of 3> warning and 4> debugging commands.

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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.