I am having to run a Microsoft cmdlet, and the important bit of information is written to console using a Write-Host line within the cmdlet.
It is NOT returned, so I cannot do $result = Commandlet ... A different value is returned that is not of use to me, what I actually need is printed to console within the commandlet is there anyway I can 'sniff' or 'scrape' the console to get the information I want?
$result = Test-Cluser
Test-Cluster will print stuff like: 'HadUnselectedTests', 'ClusterConditionallyApproved', etc. But the value it returns in the path to the .htm report file. And the .htm report file does not contain one of those status codes unfortunately so I cannot just parse the .htm file for it either.
Any suggestions?
Note: As for why you should never use Write-Host
to output data, see this answer.
In PSv5+:
$result = Test-Cluster 6>&1
Since version 5, Write-Host
writes to the newly introduced information stream, whose number is 6
.
6>&1
redirects that stream to the success output stream (number 1
), so that it too can be captured in $result
.
Caveat: The related Out-Host
cmdlet does not write to the information stream; its output cannot be captured - see this answer for the differences between Write-Host
and Out-Host
.
In PSv4-:
There is no way to capture Write-Host
output in-session.
The only workaround is to launch another instance of Powershell with the target command specified as a string.
Caveats:
Get-Help about_Redirection
$result = powershell -noprofile -command 'Test-Cluster'
Note that using a script block to pass the command (-command { Test-Cluster }
) would not work, because PowerShell then uses serialization and deserialization to emulate the in-session behavior.
Get-Help about_Redirection
discusses a list of all output streams, which can be targeted by their numbers; since PSv5, these are:
1 ... success output stream (implicit output and Write-Output output)
2 ... error output stream (Write-Error and unhandled errors)
3 ... warnings (Write-Warning)
4 ... verbose output (Write-Verbose)
5 ... debug output (Write-Debug)
6 ... (v5+) Write-Information and Write-Host output
Note that some streams are silent by default and require opt-in to produce output, either via a preference variable (e.g., $VerbosePreference
) or a common parameter (e.g., -Verbose
)
{n}>
allows redirecting the number {n}
stream; if {n}
is omitted, 1
is implied:
3> c:/tmp/warnings.txt
3> $null
)3>&1
); note: only stream 1
can be targeted this way.*>
targets all output streams.
Note: Unlike in POSIX-like shells (e.g., bash
), the order of multiple redirection expression does not matter.
Therefore, the following POSIX-like shell idiom - which redirects error output to the success stream and silences only the original success output - does NOT work:
... 2>&1 1>$null # !! NO output in PowerShell
To achieve this in PowerShell, you mustn't redirect 1
and instead filter the objects in the success by their stream of origin.
Case in point: In the end, the OP wanted the following: capture only warning output, without the regular (success) output:
Test-Cluster 3>&1 | Where-Object { $_ -is [System.Management.Automation.WarningRecord] }
Objects that came from the warning stream have type [System.Management.Automation.WarningRecord]
, which is what enables the filtering above.
I use *> instead of > to redirect all outputs from console to a file.
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