Validation: is defined whether the variable?

breeze has asked for the wisdom of the Perl Monks concerning the following question:

I have a code:

#!/usr/bin/perl

use utf8;
use warnings;
use strict;

my $var1;
my $var2 = "0";
my $var3 = 0;
my $var4 = "a";

print isDef($var1)."\n";
print isDef($var2)."\n";
print isDef($var3)."\n";
print isDef($var4)."\n";

sub isDef {
  if (shift) {
    return "true";
  } else {
    return "false";
  }
}
[download]

The result of execution is:

./test.pl 
false
false
false
true
[download]

The first variable is really undefined, but why second & third is undefined too?

p.s. Perl v5.14.1 built for i386-freebsd-thread-multi-64int

Comment on Validation: is defined whether the variable? Select or Download Code

Replies are listed 'Best First'.
Re: Validation: is defined whether the variable? by Perlbotics (Archbishop) on Aug 07, 2011 at 10:30 UTC
Because you do not test if the variable is defined but if it is true or false (0, undef, ""). Maybe you had something like this in mind? `sub isDef { return (defined shift) ? 'true' : 'false'; }` [download]	[reply] [d/l]
Re^2: Validation: is defined whether the variable? by breeze (Initiate) on Aug 07, 2011 at 10:55 UTC
But thanks, your solution is work correct ;)	[reply]
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Re: Validation: is defined whether the variable? by GrandFather (Saint) on Aug 07, 2011 at 12:12 UTC
Note that Perl has the built in function defined to make exactly the test you seem to want. If you replace isDef with defined the result will be as you seem to want. True laziness is hard work	[reply]
Re^2: Validation: is defined whether the variable? by Anonymous Monk on Aug 07, 2011 at 12:24 UTC
Um, thanks, the OP already received/accepted that answer :)	[reply]
Re: Validation: is defined whether the variable? by Anonymous Monk on Aug 07, 2011 at 10:31 UTC
Because you're not testing for definedness, you're testing for truth. See truth/true True or False? A Quick Reference Guide What is truth? (Curiosity corner) When does while() test for defined vs truth	[reply]

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