How do I filter a string array (or list) in PowerShell using the 'Match' cmdlet?

The -match operator is both a comparison operator and an array operator, depending on its input object.

If it's a scalar, it returns a boolean. If it's an array, it returns all the elements of the array that match the pattern

@($Filenames) -match '*.csv'

Use the array syntax to ensure that you still get an array if there's only one filename returned by Get-ChildItem. Otherwise, you'll get back $True instead of the filename if it matches.

Try this:

$FileNames = Get-ChildItem -Path "C:\Users\anagre\Desktop" -Filter *.csv

In your above code you didn't use the $PSItem ($_) in your where clause, and if you want to use a wildchar you have got to use the -like operator:

$FileNames|where{$_ -like "*.csv"}

or

$FileNames|where{$_ -match ".csv"}