Hmm, some time ago I learned about c#sharp by reading the source to http://sourceforge.net/projects/shellify/ ... very similar to java (probably knew that)

Searching around now I found these interesting links :) weaker ones first
A Perl developer in the world of C#
some (weak) discussion of benchmark game http://www.curmudgeonlysoftware.com/2011/03/22/from-c-sharp-to-perl-performance/
C# & Perl | Dr Dobb's / C# & Perl | Dr Dobb's

The better links are below :) Having looked at the table of contents of
C# Programming - Wikibooks, open books for an open world
C# Essentials - Techotopia
C Sharp Programming Course (aka C# Yellow Book — robmiles.com)

they compare well to the table of contents of Modern Perl by chromatic

In short, looks like they'll teach you the mechanics of the language :)

For example, what does a smart C# programmer use that a smart Perl programmer uses Getopt::Long for?

I don't know but there is a getopt from gnu project for c#sharp says http://stackoverflow.com/questions/172443/getopt-library-for-c-sharp

Likewise, what's the C# alternative to Perl's Text::CSV_XS?

Good question :) http://stackoverflow.com/questions/2081418/parsing-csv-files-in-c-sharp says FileHelpers are a free and easy to use .NET library to import/export data from fixed length or delimited records in files, strings or streams.

More generally, how would I craft the same kinds of command-line filters in C# that I'm so accustomed to whipping up quickly and easily in Perl?

http://en.wikibooks.org/wiki/C_Sharp_Programming/The_.NET_Framework/Console_Programming
http://stackoverflow.com/questions/9608591/regex-c-sharp-console-app
Category:C sharp - Rosetta Code -> http://rosettacode.org/wiki/Rot-13#C.23

So you have reading from STDIN ... checking args ... checking if files exist ... double.TryParse ... Regex regex = new Regex ... MatchCollection matches = regex.Matches(text);

That covers everything no? :)