Is Out-Host buffering?

Question

I ha a function, where I call an application with the & operator. The application produces several line command line output, downloads some files, and returns a string:

& "app.exe" | Out-Host
$var = ...
return $var

It seems, that on the console appears the output produced by app.exe only after app.exe terminates. The user does not have any real time information which file is downloading. Is there a way to continuously update the console when app.exe is running?

What if you run `"app.exe" | more` in CMD, does it show results immediately then? — user4003407, Nov 08 '16 at 13:10
Will `more` send output to the standard output? I am using `Write-Host` to prevent output data being captured in the returned variable. — robert, Nov 08 '16 at 13:11
PowerShell pipeline doesn't work like cmd for external utilities. It indeed waits for the command to complete. Simply invoke `app.exe` without `&` and `out-host`. — wOxxOm, Nov 08 '16 at 13:11
I am using `&` because the path to `app.exe` is in a variable, so I am invoking it using a string. — robert, Nov 08 '16 at 13:13
@Robert Can you answer my first question, so I can confirm my guess? — user4003407, Nov 08 '16 at 13:23
@PetSerAl, the variant using `more` does not show the result immediately. — robert, Nov 08 '16 at 13:28

score 5 · Accepted Answer · edited May 16 '23 at 11:26

Many console applications buffer theirs output stream, if it known to be redirected. Actually, it is standard behavior of C library. So, buffering is done on app.exe, because of redirection, but not by Out-Host.

A solution would be to not to redirect the output of app.exe, even when the outer command redirected. For than you should know the exact condition when PowerShell does not redirect output stream of console application and, link it directly to their own output stream, which would be a console for interactive PowerShell.exe session. The conditions is:

Command is last item in pipeline.
Command is piped to Out-Default.

Solution would be wrap command into script block, and pipe that script block to Out-Default:

& { & "app.exe" } | Out-Default

The other solution would be to use Start-Process cmdlet with -NoNewWindow and -Wait parameters:

Start-Process "app.exe" -NoNewWindow -Wait

Is Out-Host buffering?

1 Answers1

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