How to pass custom filter function to Where-Object

Question

For last hours I'm trying to figure out how to pass a scriptblock to a function to be used as a filter for where object. I haven't found any documentation, I must be missing something. I saw "filter script:" and "function:script" definitions in What is the recommended coding style for PowerShell? but I have no idea how these are used and I can't find it anywhere.

function Test
{
    Param(
            $f,     
            $What
    )

    $x = $What | where $f
    $x
}

$mywhat = @('aaa', 'b', 'abb', 'bac') 
filter script:myfilter {$_ -like 'a*'}
Test -What $mywhat -xx $myfilter

Can someone please point me to the right direction?

Frode F. · Accepted Answer · 2013-03-21 00:02:24Z

2

It's unclear what you're asking for here.

A filter is a function and not a scriptblock. where-object takes a scriptblock as an input. If you want to specify the where condition inside a function using a parameter, you could use a scriptblock-parameter.

function Test
{
    Param(
            [scriptblock]$f,     
            $What
    )

    $x = $What | where $f
    $x
}

$myfilter = {$_ -like 'a*'}
Test -What $mywhat -f $myfilter

#or combine them
Test -What $mywhat -f {$_ -like 'a*'}

If you simply wanted to use a filter, then this is how to do it:

filter script:myfilter { if($_ -like 'a*') { $_ }}

$mywhat | myfilter

That will be the equal to $mywhat | where {$_ -like 'a*'}

edited Mar 21, 2013 at 0:02

answered Mar 20, 2013 at 23:39

Frode F.

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1 Comment

JankoHrasko Over a year ago

Thanks Graimer! That's what I was looking for and I believe I have tried this in the very beginning - had to still have something wrong.

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