Weird. I've never noticed this before. There is one problem with your post (unrelated to the for (@$arrayref) working with $arraryref being undef):
If i put this line before the if, then things are ok: 
   @$arrayref;

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But thats not cool, and results in a warning too.
That can't work at all: 
#!/usr/bin/perl -w
use strict;

my $arrayref;
@$arrayref;    # line 5
print "ok";

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Useless use of a variable in void context at test.pl line 5.
Can't use an undefined value as an ARRAY reference at test.pl line 5.

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Anyway, I suggest using 

if ($arrayref) { ... }

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if $arrayref can only be false (undef) or a real ref.

update: about the if ($arrayref) test: if, as you say, arrayref should be false or an arrayref, there's no reason to do an defined() and ref() test, because if the $arrayref is true it should be an arrayref, and if it's not, there's nothing you can usefully do, except throw an exception, which is what will happen by default: 

#!/usr/bin/perl -w
use strict;

my $arrayref = 1;
for (@$arrayref) {
    print "ok\n";
}

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Can't use string ("1") as an ARRAY ref while "strict refs" in use at t
+est.pl line 5.

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"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re: Using undef scalar as arrayref by Joost
in thread Using undef scalar as arrayref by shemp

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