What type of object is $: (such as `$code:`) in Powershell?

by

What you’re seeing is namespace variable notation, which is a variable-based way to access the content of items in PowerShell drives whose underlying provider implements content-based access (i.e., implements the IContentCmdletProvider interface).

The general syntax is:

${<drive>:<path>}       # same as: Get-Content <drive>:<path>

${<drive>:<path>} = ... # same as: Set-Content <drive>:<path> -Value ...

The enclosing {...} aren’t necessary if both the <drive> name and the <path> can syntactically serve as a variable name; e.g.:

$env:HOME  # no {...} needed

${env:ProgramFiles(x86)} # {...} needed due to "(" and ")"

In practice, as of Windows PowerShell v5.1, the following in-box drive providers support namespace variable notation:

  • Environment (drive Env:)
  • Function (drive Function:)
  • Alias (drive Alias:)
  • FileSystem (drives C:, …)
  • Variable (drive Variable:) – though virtually pointless, given that omitting the drive part accesses variables by default (e.g., $variable:HOME is the same as just $HOME).

Of these, the Env: drive is by far the most frequently used with namespace variable notation, even though most users aren’t aware of what underlies an environment-variable references such as $env:HOME.

On occasion you see it used with a filesystem drive – e.g., ${c:\foo\file.txt} – but the fact that you can only use literal paths and that you cannot control the character encoding limits its usefulness.

It allows interesting uses, however; e.g.:

PS> $alias:foreach  # Get the definition of alias 'foreach'
ForEach-Object

PS> $function:prompt # Get the body of the 'prompt' function
"PS $($executionContext.SessionState.Path.CurrentLocation)$('>' * ($nestedPromptLevel + 1)) ";
# .Link
# https://go.microsoft.com/fwlink/?LinkID=225750
# .ExternalHelp System.Management.Automation.dll-help.xml

# Define a function foo that echoes 'hi' and invoke it.
PS> $function:foo = { 'hi' }; foo
hi

Note:

  • Because ${<drive>:<path>} and ${<drive>:<path>} = <value> are equivalent to
    Get-Content -Path <drive>:<path> and Set-Content -Path <drive>:<path> <value>, paths are interpreted as wildcard expressions (because that’s what -Path does, as opposed to -LiteralPath), which can cause problems with paths that look like wildcards – see this answer for an example and a workaround.

  • As of this writing, namespace variable notation isn’t officially documented yet, but this GitHub issue suggests doing so.

More Related Contents:

  1. Getting “Can’t find the drive. The drive called ‘IIS’ does not exist.”
  2. Renaming files by reformatting existing filenames – placeholders in replacement strings used with the -replace operator
  3. Unable to Pause or Sleep after Select-Object
  4. Powershell Invoke-WebRequest Fails with SSL/TLS Secure Channel
  5. How can I find the Upgrade Code for an installed MSI file?
  6. What’s the better (cleaner) way to ignore output in PowerShell? [closed]
  7. How to enter a multi-line command
  8. Add a where-object on a table construct?
  9. Is there a way to create an alias to a cmdlet in a way that it only runs if arguments are passed to the alias?
  10. Is there a way to make a PowerShell script work by double clicking a .ps1 file?
  11. Pass arguments to a scriptblock in powershell
  12. Scheduled Task Powershell Script – Runs OK as user account, but not as SYSTEM
  13. How can I do a screen capture in Windows PowerShell?
  14. Powershell color formatting with format operator
  15. Powershell string variable with UTF-8 encoding
  16. Powershell – escaping string passed to child process
  17. Calling dynamic variable in PowerShell
  18. Passing string in Get-ADUser filter parameter causes error – property not found in pscustomobject
  19. Problems using local variables in a remote commands
  20. How to get the current directory of the cmdlet being executed
  21. How to make an authenticated web request in Powershell?
  22. Powershell Log Off Remote Session
  23. $string.Substring Index/Length exception
  24. How do I compress files using powershell that are over 2 GB?
  25. How to pass a custom function inside a ForEach-Object -Parallel
  26. In what conditions does powershell unroll items in the pipeline?
  27. Connecting to a network folder with username/password in Powershell
  28. How to uninstall an app that another user installed?
  29. Uploading file to HTTP via Powershell
  30. Strange behavior for PowerShell Length after ForEach method

Leave a Comment