PowerShell script string interpolation with named parameters is not working

Question

I have the following function (I just paste it into the command line):

function Test ($url, $interface, $method)
{
   Write-Host "http://$url/$interface/$method"
}

I then call it:

Test("localhost:90", "IService", "TestMethod")

I get:

http://localhost:90 IService TestMethod//

I expect to get:

http://localhost:90/IService/TestMethod

The same thing happens if I first set the result to a variable:

$res = "http://$url/$interface/$method"
Write-Host $res

I also don't think it's due to Write-Host, since I get the same error if I pass this string into .NET objects.

It completely confuses me that this works if I just define each variable. So, it's something to do with the fact that these are function parameters. I can do this from the command line:

PS C:\> $url = "localhost:90"
PS C:\> $interface = "IService"
PS C:\> $method = "TestMethod"
PS C:\> Write-Host "http://$url/$interface/$method"
http://localhost:90/IService/TestMethod
PS C:\>

Am I doing something silly, or is there another way to do string interpolation in PowerShell?

Peter Mortensen · Accepted Answer · 2018-11-05 23:25:51Z

4

You aren't doing anything silly, but you are conflating PowerShell with something like Python.

When I do:

Function Count-Args
{
    $args.count
}

Count-args($var1, $var2, $var3)

I get a count of 1, and all three variables you put into () are cast as a single array to $args.

Just change the way you call the function to the test mysite myinterface mymethod. Note the ss64 site advice.

Don't add brackets around the function parameters:

$result = Add-Numbers (5, 10) --Wrong!
$result = Add-Numbers 5 10    --Right

edited Nov 5, 2018 at 23:25

Peter Mortensen

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answered Jul 31, 2014 at 18:31

Jason Morgan

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3 Comments

Jason Morgan Over a year ago

You don't even need to make a param block, if you keep your original function and just space the arguments like in the bottom of my example it'll work.

Mike Christensen Over a year ago

Confirmed. It's always the basic things like this that get me in PowerShell.

Jason Morgan Over a year ago

You'd probably get a lot of benefit out of an intro to Powershell book, all you have here is a common practices issue. PowerShell.org has a lot of nice free ebooks for learning PS.

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