$0      Contains the name of the file containing the Perl
             script being executed.  On some operating systems
             assigning to "$0" modifies the argument area that
             the ps(1) program sees.  This is more useful as a
             way of indicating the current program state than it
             is for hiding the program you're running.
             (Mnemonic: same as sh and ksh.)

     $|      If set to nonzero, forces a flush right away and
             after every write or print on the currently selected
             output channel.  Default is 0 (regardless of whether
             the channel is actually buffered by the system or
             not; $| tells you only whether you've asked Perl
             explicitly to flush after each write).  Note that
             STDOUT will typically be line buffered if output is
             to the terminal and block buffered otherwise.
             Setting this variable is useful primarily when you
             are outputting to a pipe, such as when you are
             running a Perl script under rsh and want to see the
             output as it's happening.  This has no effect on
             input buffering.  (Mnemonic: when you want your
             pipes to be piping hot.)

     $\      The output record separator for the print operator.
             Ordinarily the print operator simply prints out the
             comma-separated fields you specify, with no trailing
             newline or record separator assumed.  To get
             behavior more like awk, set this variable as you
             would set awk's ORS variable to specify what is
             printed at the end of the print.  (Mnemonic: you set
             "$\" instead of adding \n at the end of the print.
             Also, it's just like $/, but it's what you get
             "back" from Perl.)