-rcvs

Load the (built-in) CSV module in Ruby.

    -e

Eval the following string as Ruby code.

    CSV($<)

Create CSV parser with standard input `$<` as the source.

    .each 

Run the code in the block that follows for each row (automatically skips the CSV header):

    { |r| puts r[0] }

For a row, print the first/0th element. Can be simplified in recent Ruby:

    { puts _1[0] }