What is the Linq.First equivalent in PowerShell?
The snippet below detects from a list of files which of them is a Directory on Ftp
as C# it will be like below
var files = new List<string>(){"App_Data", "bin", "Content"};
var line = "drwxr-xr-x 1 ftp ftp 0 Mar 18 22:41 App_Data"
var dir = files.First(x => line.EndsWith(x));
How I can transalte the last line in PowerShell ?
Solution 1:
Something like this...
$files = @("App_Data", "bin", "Content")
$line = "drwxr-xr-x 1 ftp ftp 0 Mar 18 22:41 App_Data"
$dir = $files | Where { $line.EndsWith($_) } | Select -First 1
These versions of the last line would all accomplish the same:
$dir = @($files | Where { $line.EndsWith($_) })[0]
$dir = $files | Where { $line.EndsWith($_) } | Select -index 0
$dir = $files | Where { $line.EndsWith($_) } | Select -First 1
It was pointed out that the above is not exactly equivalent in behavior to Linq.First because Linq.First throws exceptions in two cases:
- Throws ArgumentNullException when source or predicate is null.
- Throws InvalidOperationException when source sequence is empty or no element satisfies the condition in predicate.
If you wanted that behavior exactly, you'd need some extra guard code.
Solution 2:
as Robert Groves said, Select-Object -First Occurence do the tricks, you can also use -Last Occurence.
by the way, like any other static .Net method you can use linq in powershell.
[Linq.Enumerable]::First($list)
[Linq.Enumerable]::Distinct($list)
[Linq.Enumerable]::Where($list, [Func[int,bool]]{ param($item) $item -gt 1 })
Solution 3:
Doug Finke produced a great video ( only 7 mins ) about converting C# to Powershell http://dougfinke.com/video/CSharpToPowerShell.html
Roberts example is very good indeed, though comma delimiting will implicitly be treated as an array
the shortest way of doing it would be to put it all into a single pipeline :
$dir = "App_Data", "bin", "Content" | % { if("drwxr-xr-x 1 ftp ftp 0 Mar 18 22:41 App_Data".EndsWith($_)) { $_ } } | select -first 1