The Where-Object cmdlet is incredibly powerful, in that it allows you to filter your output based on arbitrary criteria. For extremely simple filters (such as filtering based only on a comparison to a single property,) though the syntax can get a little ungainly:
get-process | where { $_.Handles -gt 1000 }
For this type of situation, it is easy to write a function to offload all of the syntax to the function itself:
get-process | wheres Handles gt 1000
dir | wheres PsIsContainer
The following snippet implements the “simple where” functionality:
function wheres($property, $operator = "eq", $matchText = "$true")
{
Begin { $expression = "`$_.$property -$operator `"$matchText`"" }
Process { if(invoke-expression $expression) { $_ } }
}
Much better!
Note: although extremely simple, this solution can be improved. Since we pass arbitrary input to the Invoke-Expression cmdlet, it is quite easy to make syntactic mistakes that foul up the call to Invoke-Expression. Also, this function can be abused if you don’t fully trust the input that you pass it:
dir | wheres PsIsContainer eq 'False" -and (write-host "Hello") -and "'
Bruce Payette expands on this function (and problem) in his upcoming book, “PowerShell in Action.”