Writing errors and output to a text file and Console

By default only the Success stream of data is passed on to the Output file. To direct errors and warnings you will have to add something like this :

your script 3>&1 2>&1 | Out-file log.txt

I couldn't get both errors and results in the same file. A workaround that worked for me:

.\MyScript.ps1 2> C:\errors.txt | tee -filePath C:\results.txt

Update: I have worked further and I used Start-Transcript and Stop-Transcript in my mode to capture everything and it worked!

I wasn't satisfied with any answer I was finding, so I mixed a few and came up with this (in PowerShell 3.0+):

$output = try{your_command *>&1}catch{$_}

With this you can capture all errors and output that are generated by trying to use your_command.

It catches exceptions when you use a non-existent command:

PS C:\Users\jdgregson> $output = try{your_command *>&1}catch{$_}
PS C:\Users\jdgregson> echo $output
your_command : The term 'your_command' is not recognized as the name of a
cmdlet, function, script file, or operable program. Check the spelling of the
name, or if a path was included, verify that the path is correct and try again.
At line:1 char:15
+ $output = try{your_command 2>&1}catch{$_}
+               ~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (your_command:String) [], Comman
   dNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

PS C:\Users\jdgregson>

It catches exceptions when you pass invalid arguments to an existing command:

PS C:\Users\jdgregson> $output = try{cat C:\invalid-path.txt *>&1}catch{$_}
PS C:\Users\jdgregson> echo $output
cat : Cannot find path 'C:\invalid-path.txt' because it does not exist.
At line:1 char:15
+ $output = try{cat C:\invalid-path.txt 2>&1}catch{$_}
+               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (C:\invalid-path.txt:String) [Ge
   t-Content], ItemNotFoundException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetCo
   ntentCommand

And it catches the output if there was no problem with your command at all:

PS C:\Users\jdgregson> $output = try{cat C:\valid-path.txt *>&1}catch{$_}
PS C:\Users\jdgregson> echo $output
this file is really here

It works for your example too:

PS C:\Users\jdgregson> $output = try{Test-Error *>&1}catch{$_}
PS C:\Users\jdgregson> echo $output
echo
WARNING: warning
Test-Error : error
At line:1 char:15
+ $output = try{Test-Error *>&1}catch{$_}
+               ~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Write-Error], WriteErrorExcep
   tion
    + FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorExceptio
   n,Test-Error

Have you tried:

 .\MyScript.ps1 2>&1 | tee -filePath c:\results.txt

2>&1 is what you're looking for

Note: This answer works great in PowerShell 1.0 and 2.0, but will capture ONLY standard output and errors in PowerShell 3.0 and later.