This is a problem that is more pronounced with hashes. It is possible for a hash key to exist but have an undefined value. The general rule is: use define() to test for array elements and use exist() to test for hash elements.

my @fred = ();
$fred[999] = ‘somevalue’;

then $fred[0..998] do not exist.

#!/usr/bin/perl

use strict;
use warnings;

my @fred = ();
$fred[9] = ‘somevalue’;

for my $i ( 0 .. $#fred ){
if( exists $fred[$i] ){
if( defined $fred[$i] ){
print “\$fred[$i] exists, is defined, and has value $fred[$i]\n”;
}else{
print “\$fred[$i] is not defined\n”;
}
}else{
print “\$fred[$i] does not exists\n”;
}
}

13) Always have a return statement for your sub’s. That way you always know what is returned.

sub foo {
return;
}

If foo() is called in a scalar context, undef is returned. If it is called in a list context, the empty list, (), is returned.

sub bad_return {
return undef;
}

In a list context, this will return a list of one element: ( undef ) This is not the empty list.

14) All the special Perl variables can be found here: http://perldoc.perl.org/perlvar.html

Plus:

Always `use strict;` It will cause a fatal compile error for most things you do not want to do.

fREW Schmidt, wouldn’t be using “use warnings;” are more gentle to newbies because i have tried a few times turning on “use strict;” and it throw a bunch of errors to me which i dont understand it. Rather, using “use warnings;”, the suggestions are more gentle and easier to understand.

just my 2 cents.

[He is reading] _Learning Perl_, and he hasn’t got to the point where we tell the reader they don’t need the & in front of subroutine calls. Most of the progression goes from the general rule to the usual case.

I don’t find his argument compelling as I don’t consider &foo() the general rule, but more of an exception to the general case that has magical behavior.