in reply to Or, Or, Equals Zero, $x ||= 0
The reason for using that expression is probably that the original script author was (wisely) including a "-w" flag on the shebang line, or put "use warnings;" near the top of the script. In those cases, the $x ||= 0; will prevent perl from issuing a warning about "use of undefined value in numeric comparison" or "use of undefined value in print".
Works for strings too: $x ||= '': will avoid warnings about using an undefined value in a print, string concatenation, string comparison, regular expression, and so on.
It's not that undefined values are inherently bad -- sometimes you want a variable to be undef, and if you really want to use undef values in a print or a comparison to some actual value, you can modify the "use warnings" pragma to say which warnings it should ignore. But such "special needs" cases are pretty rare (and probably avoidable).
In Section Seekers of Perl Wisdom