How to pass dynamic parameters in Powershell?

Question

I want to call an existing commandlet with a dynamic number of parameters.

So instead of doing this (taking write-host as an example), I would like to do it the smart way.

# these are the dynamic parameters which maybe get passed into my function or script
# they would be $null be default of course
$forecolor = 'Green'
$newline = $true

# now build the "dynamic" write-host...
if ($forecolor) {
    if ($newline) {
        write-host -fore $forecolor "Hello world"
    }
    else {
        write-host -fore $forecolor "Hello world" -nonewline
    }
}
else {
    if ($newline) {
        write-host "Hello world"
    }
    else {
        write-host "Hello world" -nonewline
    }
}

This of course is very ugly. Help me make it prettier!

I already tried just setting $forecolor = '-fore Green' which only outputs "-fore Green Hello world". I could think of passing a list of arguments to a function and for each argument in the list add the according parameter - I just don't know how to hold the parameters.

Have you had a look at parameter sets? blogs.technet.com/b/heyscriptingguy/archive/2011/06/30/… — David Brabant
– David Brabant, Commented Jun 22, 2012 at 8:14

Joey · Accepted Answer · 2012-06-22 08:18:50Z

21

You can just pass your variables as arguments to Write-Host:

Write-Host -Fore $forecolor -NoNewLine:(!$newline) 'Hello World'

For a truly dynamic way you can use a hashtable:

$params = @{ NoNewLine = $true; ForegroundColor = 'Green' }

and then use the splat operator

Write-Host @params Hello World

You can add parameters and their values to the hashtable as you like before calling Write-Host that way.

answered Jun 22, 2012 at 8:18

Joey

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3 Comments

Dennis G Over a year ago

Awesome! Here's an article about splatting: technet.microsoft.com/en-us/magazine/gg675931.aspx never heard of that wizardry before. Thanks.

Patrick Over a year ago

I have been working for years with PowerShell and have never heard about this. Now finally, I did: Great feature!

Eric Eskildsen Over a year ago

Your last example already implies this, but just for clarity, you can mix and match as well: Write-Host @params Hello World -BackgroundColor White

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