[oak perl] The mysterious "undef"

[Kester Allen]

Hi Sandy--

Here's a quickie example of a way to detect undef-- test for it with
"defined", and then print something based on the result of that:

$x = undef; 
print "x is undef\n" if not defined $x; 
$y = 0; 
print "y is defined\n" if defined $y"

One place I run into undef frequently is in subroutines optional
arguments.  I.e. if you called a sub like:

sub test {
    my ( $x, $y, $z ) = @_;
}

with "test( 1, 2)", $x would be 1, $y would be 2, and $z would be
undef (not zero).

perldoc -f defined has some good text on this.

--Kester

On Fri, 18 Mar 2005 11:10:22 -0500, Sandy Santra <santranyc at yahoo.com> wrote:
> I keep seeing "undef" mentioned in the llama book.
> 
> I've tried to define a variable as not having a value, theoretically being
> "undef," but when I use the print command, I never see "undef" print to my
> screen; nothing prints at all.
> 
> I wanted to learn the different between a zero value and undef because the
> llama book keeps saying there is one.  Is this a pointless issue to pursue?
> 
> Clarification greatly appreciated.  Thanks.
> 
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