Running help <command> and piping output to Where-Object or Select-Object returns empty rows

Question

Running the command help firewall | Select-Object Category help firewall | Select-Object Category . The result is one column blank Category .

The strange thing is that the empty rows number represent the amount of rows that help firewall would result without calling piping it to Select-Object

Or I'm trying to filter the output of help firewall to return only rows with Name that starts with "Get". Running help firewall | Where-Object Name -like "Get" help firewall | Where-Object Name -like "Get" just returns nothing.

Why aren't these pipes on help working? They are working perfectly on other commands.

Powershell Version 5.1 and using default windows console.

Answer 1

To complement Zilog80's helpful answer with background information:

Get-Command help reveals that help is not a mere alias of the Get-Help cmdlet, but a (built-in) function (submit $function:help to see its definition).

As you've noticed yourself:

• while Get-Help outputs an object ( [pscsustomobject] ) with properties that reflect help-topic metadata such as Category , which is then rendered as display text by PowerShell's output-formatting system,

• the help function returns strings - a stream of text lines representing the rendered help topic - of necessity.

You can observe the difference in output type by piping to the Get-Member cmdlet ( help firewall | Get-Member vs. Get-Help firewall | Get-Member )

The purpose of the help function is to wrap Get-Help with interactive paging , to allow convenient navigation through lengthy help topics that don't fit onto a single console (terminal) screen.

This paging is provided via an external program (by default, more.com on Windows, and less on Unix-like platforms, configurable via $env:PAGER , but only in PowerShell (Core) 7+ ), and since PowerShell only "speaks text" when communicating with external programs, help must send a stream of strings (lines for display) to them, which it does via
Out-String -Stream .

Note:

• When the external paging programs find that their stdout stream isn't connected to a console (terminal), they take no action other than simply passing the input through (in Unix terms, they then behave like cat ).

• Hypothetically, the help function itself could determine this condition and then (a) not pipe to the paging program and (b) relay the object output by Get-Help as-is. ^[1] However, determining a command's output target from inside that command, using PowerShell code, may not even be possible.

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^{[1] The function actually already takes this action when a custom pager defined via $env:PAGER is found to be a PowerShell command rather than an external program.}

Answer 2

Check the feedback from help help in PowerShell:

    You can also type `help` or `man`, which displays one screen of text at a
    time. Or, ` -?`, that is identical to `Get-Help`, but only
    works for cmdlets.

The help command display "screen of text" which means it is outputting [System.String] objects, not [PSCustomObject] objects.

Only -? will behave identically to Get-help and will provide [PSCustomObject] objects.

To see what's going on, check the different output from:

help firewall | %{ $_.GetType() }

And

Get-help firewall | %{ $_.GetType() }

And, for cmdlet,

Select-Object -? | %{ $_.gettype() }