Re: Logical expression evaluation

In Perl, the logical values are typically 1 for truth, and undef for falsehood. When treated as a number, undef == 0, when treated as a string, undef eq '', all of which are treated as a false in boolean condition checks.

--
[ e d @ h a l l e y . c c ]

Comment on Re: Logical expression evaluation Select or Download Code

Replies are listed 'Best First'.
Re^2: Logical expression evaluation by ikegami (Patriarch) on Jul 27, 2005 at 16:26 UTC
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 []` [download]	[reply] [d/l] [select]
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]