Re^2: Logical expression evaluation

As mentioned earlier in this thread, Perl uses "" for false. It does not use undef.

$i = undef;  print(defined($i) ? "[$i]" : 'undef', "\n");
$i = !1;     print(defined($i) ? "[$i]" : 'undef', "\n");

__END__
output
------
undef
[]
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Re: Logical expression evaluation by benizi (Hermit) on Jul 27, 2005 at 20:55 UTC
Wrong. Perl false is !1. (PL_sv_no in the C source) It's a dualvar with a string value of "" and a numerical value of 0. See: Re^4: m//g behaves strange... (!1). And this snippet: Read more... (833 Bytes)	[reply] [d/l]
Re^2: Logical expression evaluation (dualvar) by bart (Canon) on Jul 27, 2005 at 21:07 UTC
And nowadays, you can have the magic of dualvars for your own ~~evil plots~~ applications, using dualvar() from Scalar::Util. BTW another typical magical dualvar value is $!, which returns an error message as a string, and an error number as a number. For example: `local $\ = "\n"; $! = 3; # error number print $!; # error message print 0+$!; # error number` [download]	[reply] [d/l]