How to redirect the output of a PowerShell to a file during its execution

I have a PowerShell script for which I would like to redirect the output to a file. The problem is that I cannot change the way this script is called. So I cannot do:

 .\MyScript.ps1 > output.txt

How do I redirect the output of a PowerShell script during its execution?

Maybe Start-Transcript would work for you. First stop it if it's already running, then start it, and stop it when done.

$ErrorActionPreference="SilentlyContinue"
Stop-Transcript | out-null
$ErrorActionPreference = "Continue"
Start-Transcript -path C:\output.txt -append

Do some stuff
Stop-Transcript

You can also have this running while working on stuff and have it saving your command line sessions for later reference.

If you want to completely suppress the error when attempting to stop a transcript that is not transcribing, you could do this:

$ErrorActionPreference="SilentlyContinue"
Stop-Transcript | out-null
$ErrorActionPreference = "Continue" # or "Stop"

Microsoft has announced on Powershell's Connections web site (2012-02-15 at 4:40 PM) that in version 3.0 they have extended the redirection as a solution to this problem.

In PowerShell 3.0, we've extended output redirection to include the following streams: 
 Pipeline (1) 
 Error    (2) 
 Warning  (3) 
 Verbose  (4) 
 Debug    (5)
 All      (*)

We still use the same operators
 >    Redirect to a file and replace contents
 >>   Redirect to a file and append to existing content
 >&1  Merge with pipeline output

See the "about_Redirection" help article for details and examples.

help about_Redirection

Use:

Write "Stuff to write" | Out-File Outputfile.txt -Append

I take it you can modify MyScript.ps1. Then try to change it like so:

$(
    Here is your current script
) *>&1 > output.txt

I just tried this with PowerShell 3. You can use all the redirect options as in Nathan Hartley's answer.

powershell ".\MyScript.ps1" > test.log

One possible solution, if your situation allows it:

1. Rename MyScript.ps1 to TheRealMyScript.ps1

2. Create a new MyScript.ps1 that looks like:

   .\TheRealMyScript.ps1 > output.txt

If you want a straight redirect of all output to a file, try using *>>:

# You'll receive standard output for the first command, and an error from the second command.
mkdir c:\temp -force *>> c:\my.log ;
mkdir c:\temp *>> c:\my.log ;

Since this is a straight redirect to file, it won't output to the console (often helpful). If you desire the console output, combined all output with *&>1, and then pipe with Tee-Object:

mkdir c:\temp -force *>&1 | Tee-Object -Append -FilePath c:\my.log ;
mkdir c:\temp *>&1 | Tee-Object -Append -FilePath c:\my.log ;

# Shorter aliased version
mkdir c:\temp *>&1 | tee -Append c:\my.log ;

I believe these techniques are supported in PowerShell 3.0 or later; I'm testing on PowerShell 5.0.

You might want to take a look at the cmdlet Tee-Object. You can pipe output to Tee and it will write to the pipeline and also to a file

If you want to do it from the command line and not built into the script itself, use:

.\myscript.ps1 | Out-File c:\output.csv

To embed this in your script, you can do it like this:

		Write-Output $server.name | Out-File '(Your Path)\Servers.txt' -Append

That should do the trick.