• $/ is the input record separator. This is "\n" by default.
• $\ is the output record separator. This is the empty string by default. Setting it to $/ means that you no longer need to put a "\n" on the end of each print statement.
• $, is the string that is output between each element of the list passed to print. The default value is the empty string. By setting it to ":" we don't just control the split statement, but also the print statement. The elements of @f are printed separated by ":" characters.

Does that help? You can get more info on special Perl variables like these in perlvar.

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"The first rule of Perl club is you don't talk about Perl club."