You can use that feature for less-magic numbers in quick scripts. Eg:

my $time = $minutes / '60 minutes per hour' / '8 hour workdays';

Aha ! Thanks, good answer !

pmarcoen:

The statement isn't necessarily wrong--perl does automatic conversions between numbers and strings, and strings that don't "look like a number" get converted to 0 when you treat them like a number. After all, in a data stream, there may be multiple different data types that you would want to handle differently without lots of explicit type conversions and such. (If you're a fan of explicit conversions, perhaps you should be a Java programmer? </joke>)

Here's a simple (useless!) example of treating different types of data differently:

$ cat 938362.pl
#!/usr/bin/perl
use strict;
use warnings;
use Scalar::Util qw(looks_like_number);

my $t;
while ($t = <DATA>) {
    $t=~s/\s+$//;
    print "\ninput = '$t'\n";
    if (looks_like_number($t)) {
        print "looks numeric\n";
        if ($t == 0) {
            print "Gotta have somethin' if ya wanna be with me\n";
        }
        else {
            print "There are $t ways to leave your lover\n";
        }
    }
    else {
        print "non-numeric\n";
        if ($t eq "Godzilla") {
            print "Oh, no! There goes Tokyo, go go $t!\n";
        }
        elsif ($t =~ /horse/i) {
            print "A horse is a horse of course, of course\n";
        }
        else {
            print "insert song lyric here...\n";
        }
    }
}
__DATA__
Godzilla
50
A horse of a different color
0
zebra
$ perl 938362.pl

input = 'Godzilla'
non-numeric
Oh, no! There goes Tokyo, go go Godzilla!

input = '50'
looks numeric
There are 50 ways to leave your lover

input = 'A horse of a different color'
non-numeric
A horse is a horse of course, of course

input = '0'
looks numeric
Gotta have somethin' if ya wanna be with me

input = 'zebra'
non-numeric
insert song lyric here...
[download]

Since using text strings where numbers are expected is a common logic error, the warnings package tells you when you try to convert a string that doesn't look like a number into a number.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

It seems to me that if a statement is wrong, it should not evaluate to true, what am I missing here?

• Your syntax is incorrect. In that case, it won't compile, it won't run, and it certainly doesn't evaluate to true.
• You do something Perl cannot do, or has been forbidden to do. Dividing by zero for instance, or dereferencing a string while "use strict 'refs'" is active. In that case, Perl will throw an exception - it will not continue with false (besides, what should be false? A term of the expression? The expression? The block? The current subroutine?). Although one may say that if the exception isn't dealt with, Perl evaluates the entire program to false. ;-)
• You used the wrong (business) logic. How's Perl supposed to know? You might as well ask Gravity to not shatter the priceless vase if you dropped it by accident instead of intentionally.

Time for the obligatory link to perlsyn. Specifically in the Truth and Falsehood section, you will find:

The number 0, the strings '0' and '' , the empty list () , and undef are all false in a boolean context. All other values are true. Negation of a true value by ! or not returns a special false value. When evaluated as a string it is treated as '' , but as a number, it is treated as 0.

use strict; use warnings;

if('test' eq 0){  print "in if"   }
else           {  print "in else" }

if(!'test')    {  print "again in if"   }
else           {  print "again in else" }

__END__

prints: in else again in else
[download]

All strings in perl are evaluated to true (even the string 'false'!) except this: '0'

if('0' eq 0)  {  print "in if"   }
else          {  print "in else" }

__END__

prints: in if
[download]

the problem here is that you are trying to mix a boolean and a number, this is a logical operation, the same as if(TRUE is FALSE)... not numerical as in if (2*4 == 8), you are trying to say: if (TRUE == 8)

If you really want to specify that 'this_chain' == zero (the number) and force a numeric comparison you need to comment and deactivate use warnings, (but this is nonsense, use a variable name instead)

Updated: if ($var == 0) is not a problem for warnings, of course