Explain PowerShell code

What this PowerShell sample shows

cmdlets and the pipeline

Get-ChildItem lists the files, | hands each one to Where-Object, which keeps the ones that pass its test, and Sort-Object Length -Descending puts the biggest first. -Filter *.log and -File narrow the list before anything reaches the pipeline, so notes.txt and the folders never show up.

objects and properties

The pipeline passes file objects, not lines of text. Inside { ... }, $_ is the current file, so $_.LastWriteTime and $_.Length are its date and size, with no text to cut apart. @{ Name = "SizeKB"; Expression = { ... } } adds a column worked out for each file, and 1KB is PowerShell's own constant for 1,024.

parameters

param() declares what the script takes. [Parameter(Mandatory)] made a run with no -Path stop with missing mandatory parameters: Path, [int] made -Days abc stop with Cannot convert value "abc" to type "System.Int32", and = 30 is the default when -Days is left out.

WhatIf and ShouldProcess

[CmdletBinding(SupportsShouldProcess)] gives the script a -WhatIf switch. $PSCmdlet.ShouldProcess(...) returns false under -WhatIf and prints the change instead, so the run printed What if: Performing the operation "Delete" on target ... for each old log and deleted nothing.

Good to know

• Run with PowerShell 7.6.9 on four test files, two .log files from 20 September, one from 4 November and a .txt, with -Days 30 -WhatIf on 5 November: it listed the two September logs, printed 2 files, 250.0 KB and left all four files in place.
• The same run without -WhatIf, on a copy of the folder, deleted exactly those two logs and kept notes.txt and the November log.
• With one old file the summary read 1 files, 2.0 KB, and with none 0 files, 0.0 KB. .Count works on a single result and on an empty one in PowerShell 7, so the line never breaks.

Watch out: Use -LiteralPath for file names you didn't type. In a file called app[1].log, -Path reads [1] as a wildcard: Remove-Item -Path matched nothing, deleted nothing and still reported success, while -LiteralPath removed the file.