Yes, $num =~ /[02468]$/ (...with the proviso that some may consider that 0 (zero) is neither odd nor even).
Yes, the function eof tells you if you are at the end of a file. In practise, you never need to use it, you simply keep on reading until you fall off the end.
No, but if you are running on a Unix variant you should have the uniq command at your disposal, and it will probably run much faster than the Perl one-liners mentioned elsewhere in this thread. Using uniq has another advantage: if on occasion a line is not followed by a duplicate, it will emit both lines. The modulo-2 approach, on the other hand, will get out of sync and begin throwing away good data.
- another intruder with the mooring of the heat of the Perl