How to change Get-Date commandlet default result value in Powershell

Question

Get-Date returns something like "26 July 2023 12:54:21"

this is the default representation (it is the content of property .DateTime which is a string)

how can I set the default result of Get-Date to .Year (for example)

• This is a generic types question but I think is better to put it this way
• Update-TypeData did not solve this problem... just for Format-List/Table/Wide...
• I know I can do (get-date).year... that is not the point!

Answer 1

Note:

• This answer addresses how to change the representation of [datetime] (System.DateTime) instances (such as output by Get-Date) when converted to strings, either explicitly or implicitly.

• This has no impact on using [datetime] instances as themselves.

---

You can use Update-TypeData to both modify the .DateTime ScriptProperty ETS (Extended Type System property of [datetime] instances and to override the type-native .ToString() method with a ScriptMethod ETS property, but there's a wrinkle:

• Due to a bug, present up to at least PowerShell 7.3.9 (current as of this writing), in the context of [string] casts and PowerShell's string interpolation (inside expandable (double-quoted) strings ("...")) an ETS .ToString() method is unexpectedly not honored - see GitHub issue #14561; sadly, it appears that this bug won't get fixed.

# Override .ToString()
Update-TypeData -Force -TypeName System.DateTime -MemberType ScriptMethod -MemberName ToString -Value {
  [string] $this.Year
}
# Redefine .DateTime
Update-TypeData -Force -TypeName System.DateTime -MemberType ScriptProperty -MemberName DateTime -Value {
  $this.ToString() # This calls the overridden .ToString() method.
}

Now, the .DateTime property of [datetime] instances reports just the instance's year, and so do (explicit and implicit) .ToString() calls:

# === These work:
# Use of the redefined .DateTime via the formatting system.
Get-Date
[datetime]::Now
# Use of the overridden .ToString() method.
(Get-Date).ToString()
Write-Host (Get-Date) # implicit .ToString() call 
[pscustomobject] @{ Date = (Get-Date) } # implicit .ToString() call on nested values

# === Due to the BUG mentioned above, the following do NOT work.
# They use the original .ToString() format.
"$(Get-Date)"
[string] (Get-Date)