Re: Or, Or, Equals Zero, $x ||= 0

[graff]

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).

[tye]

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.

That also turns '0' into '' and so would probably be better written as:

$x= ''  if ! defined $x;

Or you can use //= if you are on the bleading edge and eschew backward compatability. Note that ||= is probably the best choice for the numeric case as treating '' as a number can also cause a warning.

[Erez]

If it's on a new code, and no animals are harmed, I don't see a problem with using 5.10 syntax. It's a question of what the people around you like to read. For instance, I'd write it

$x= ''  unless defined $x;

But its a question of whatever suits.