From perlvar:

     $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.)
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{
    local $/ = undef;
    $_ = <FH>;
}
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Here's the entry from perlvar:

     $/      The input record separator, newline by default.
             Works like awk's RS variable, including treating
             empty lines as delimiters if set to the null string.
             (Note: An empty line cannot contain any spaces or
             tabs.)  You may set it to a multi-character string
             to match a multi-character delimiter, or to undef to
             read to end of file.  Note that setting it to "\n\n"
             means something slightly different than setting it
             to "", if the file contains consecutive empty lines.
             Setting it to "" will treat two or more consecutive
             empty lines as a single empty line.  Setting it to
             "\n\n" will blindly assume that the next input
             character belongs to the next paragraph, even if
             it's a newline.  (Mnemonic: / is used to delimit
             line boundaries when quoting poetry.)

                 undef $/;
                 $_ = <FH>;          # whole file now here
                 s/\n[ \t]+/ /g;

             Remember: the value of $/ is a string, not a regexp.
             AWK has to be better for something :-)
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• $0 ($PROGRAM_NAME)
  The name of the file containing the running perl script.
• $| ($OUTPUT_AUTOFLUSH)
  Causes a fflush after each write or print if true. Usually set in cgi scripts by $|++ or $|=1;
• $\ ($OUTPUT_RECORD_SEPARATOR)
  Similar to awk's ORS. Rarely used.

The parenthesis are the "English" names (you can use those if you say

use English;
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