• $0 ($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;
[download]

at the top of your script).