In Powershell, out-file doesn't redirect write-host from start-job and invoke-command

Question

I distilled this from a larger script. The problem I'm having is that the out-file doesn't work to save "sdfsdfad" to a file and instead prints to the console "sdfsdfad".

    $ErrorActionPrefence   = "Stop"

    $s1=@'
        for($i=0; $i -lt 10; $i++) {
            write-host "sdfsdfad"
        }

    '@

    $s1 > $env:userprofile\Documents\s1.ps1

    $sb = {
        $ErrorActionPreference   = "Stop"

        Set-PSDebug -Trace 0
    
        $alog = "$env:userprofile\Documents\a2.txt"
    
        $null > $alog    

        invoke-expression $env:userprofile\Documents\s1.ps1 | out-file -Append $alog
    }

    start-job -ScriptBlock $sb | Receive-job -wait

    Get-Content $env:userprofile\Documents\a2.txt

Console Output that is suppose to be in "~\Documents\a2.txt" instead:

sdfsdfad
sdfsdfad
sdfsdfad
sdfsdfad
sdfsdfad
sdfsdfad
sdfsdfad
sdfsdfad
sdfsdfad
sdfsdfad

`Write-Host` goes to the `Information Stream`. Redirect it to stdout if you want to capture it's output `6>&1 | Out-File ...` — Santiago Squarzon, Nov 04 '21 at 19:56
Does this answer your question? [PowerShell Capture Write-Host output](https://stackoverflow.com/questions/50937190/powershell-capture-write-host-output) — Santiago Squarzon, Nov 04 '21 at 19:58

mklement0 · Answer 1 · 2021-11-05T14:04:05.350

Don't use Write-Host to output data - use Write-Output or, preferably, implicit output.
Don't use Invoke-Expression to call scripts and avoid it in general - use &, the call operator, to call a command whose name or path is based on a variable or quoted.

In cases where you don't have control over a script that uses Write-Host, you can use 6>&1 to redirect that output to the success output stream in order to send it through the pipeline, so that Out-File saves it.
Note that this only works in PowerShell v5 and above.

See this answer for more information about capturing Write-Host output, and this answer for information about redirection syntax such as 6>&1.

Applied to your code (if you really must stick with Write-Host):

& $env:userprofile\Documents\s1.ps1 6>&1 | out-file -Append $alog

Or, more simply, given that >> is effectively an alias of Out-File -Append:

& $env:userprofile\Documents\s1.ps1 6>&1 >> $alog

Note:

Unlike in POSIX-compatible shells such as bash, the order of the redirections does not matter.
You can merge multiple streams selectively into the success output stream, or simply target all streams (see below).

Or, even simpler, to catch all (*) output streams:

& $env:userprofile\Documents\s1.ps1 *>> $alog

I guess my bad on voting for closure due to duplicate answer, tho I do feel OP is hardly listening to the advice we're giving hehe — Santiago Squarzon, Nov 04 '21 at 20:05
@SantiagoSquarzon, closing it as a duplicate would definitely have been an option. However, I wanted to call out the anti-patterns in the question explicitly (not least because the OP has misused `Invoke-Expression` before, at which time I only called it out in a comment, which was ignored). — mklement0, Nov 04 '21 at 20:10

In Powershell, out-file doesn't redirect write-host from start-job and invoke-command

1 Answers1