What does the "@" symbol do in Powershell?

Question

I've seen the @ symbol used in PowerShell to initialise arrays. What exactly does the @ symbol denote and where can I read more about it?

Answer 1

The Splatting Operator

To create an array, we create a variable and assign the array. Arrays are noted by the "@" symbol. Let's take the discussion above and use an array to connect to multiple remote computers:

$strComputers = @("Server1", "Server2", "Server3")

They are used for arrays and hashes.

PowerShell Tutorial 7: Accumulate, Recall, and Modify Data

Array Literals In PowerShell

Answer 2

PowerShell will actually treat any comma-separated list as an array:

"server1","server2"

So the @ is optional in those cases. However, for associative arrays, the @ is required:

@{"Key"="Value";"Key2"="Value2"}

Officially, @ is the "array operator." You can read more about it in the documentation that installed along with PowerShell, or in a book like "Windows PowerShell: TFM," which I co-authored :).

Answer 3

You can also wrap the output of a cmdlet (or pipeline) in @() to ensure that what you get back is an array rather than a single item.

For instance, dir usually returns a list, but depending on the options, it might return a single object. If you are planning on iterating through the results with a foreach-object, you need to make sure you get a list back. Here's a contrived example:

$results = @( dir c:\autoexec.bat)

One more thing... an empty array (like to initialize a variable) is deonted @().

Answer 4

Also used for here-strings:

http://blogs.msdn.com/powershell/archive/2008/09/14/rdp-file-generation-use-of-here-strings.aspx http://blogs.msdn.com/powershell/archive/2006/07/15/Variable-expansion-in-strings-and-herestrings.aspx http://www.microsoft.com/technet/scriptcenter/resources/pstips/jun07/pstip0629.mspx

And Splat:

http://bartdesmet.net/blogs/bart/archive/2008/03/24/windows-powershell-2-0-feature-focus-splat-split-and-join.aspx

Answer 5

What about this usage of the @ symbol:

Import-Csv $file.Name | Select-Object -Property Col1, Col2, @{Name="NewCol";Expression={$newColVal}}, Column3

In this instance it's used to add a column to the imported CSV, but can someone explain why/how?

Answer 6

In PowerShell V2, @ is also the SPLAT operator.

PS> # First use it to create a hashtable of parameters:
PS> $params = @{path = "c:\temp"; Recurse= $true}
PS> # Then use it to SPLAT the parameters - which is to say to expand a hash table 
PS> # into a set of command line parameters.
PS> dir @params
PS> # That was the equivalent of:
PS> dir -Path c:\temp -Recurse:$true

Experiment! Enjoy! Engage!

Jeffrey Snover [MSFT] Windows Management Partner Architect