PowerShell LINQ with Short Aliases

2019-07-15 17:04 UTC
.NET C# LINQ PowerShell

Most modern applications or code today deal with some kind of filtering or querying. In C# and .NET, we have Language Integrated Query (LINQ), which we also have access to in PowerShell, because it's built on .NET.

To list the top 10 largest files in the Windows temporary folder, which is larger than 1 Mb and starts with the letter W, skipping the first 5, ordering by size, the C#-code with LINQ would look somewhat like this:

new System.IO.DirectoryInfo(@"C:\Windows\Temp")
    .GetFiles()
    .Where(x => x.Length > 1024 && x.Name.StartsWith("W"))
    .OrderByDescending(x => x.Length)
    .Select(x => new { x.Name, x.Length })
    .Skip(5)
    .Take(10)
    .ToList()
    .ForEach(x => Console.WriteLine($"{x.Name} ({x.Length})"));

The equivalent logic in PowerShell has a bit of a more daunting syntax, especially if you're not used to it:

Get-ChildItem "C:\Windows\Temp" `
| Where-Object {$_.Length -gt 1024 -and $_.Name.StartsWith("W")} `
| Sort-Object {$_.Length} -Descending `
| Select-Object -Property Name, Length -First 10 -Skip 5 `
| ForEach-Object {Write-Host "$($_.Name) ($($_.Length))"}

That's a bit explicit and verbose, but if you use the command Get-Alias in PowerShell, you will see a lot of useful aliases, which make the syntax a bit terser and easier to get an overview of:

gci "C:\Windows\Temp" `
| ?{$_.Length -gt 1024 -and $_.Name.StartsWith("W")} `
| sort{$_.Length} -Descending `
| select Name, Length -First 10 -Skip 5 `
| %{write "$($_.Name) ($($_.Length))"}

In a real scenario, you probably wouldn't write each result to the console, but let PowerShell present the result in its default grid format.

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