Hi, so one of the greatest things about Perl is its documentation. You can find answers yourself!

I Googled for 'perl ++ operand' and got perlop - Perl operators and precedence > Auto increment and Auto decrement. (Here we increment the value stored in %seen for each key *before* making sure that we haven't already seen this key by checking that the value *after* incrementing is less than 2. Also makes use of Perl's autovivification.)

For -n and -E and all other command line switches for the perl executable, see perlrun - how to execute the Perl interpreter.

Note that the doc I first pointed you to, perlintro, contains links to all these docs in the overview it gives of each topic. Have you yet allocated a couple of hours of your time to read that document? Seems fair, when you are getting other Monks to give of their time to you.